When asked to describe his contribution to Torah scholarship, R. Chayim Brisker was wont to say: "Before my approach to study became popular, people would bring bricks to shevah berachos."
He would explain: With regard to the laws of ritual purity, the Talmud uses the term ponim chadashos in reference to bricks, i.e., if bricks are made from straw which is impure, the bricks are, nevertheless, considered pure, because ponim chadashos ba'u lekan. The bricks are a new entity, so different from the straw that the straw's state of ritual impurity is of no significance.
With regard to shevah berachos, it is necessary that ponim chadashos, people who had not attended the wedding ceremony, participate for the shevah berachos to be recited.
"I taught people," R. Chayim would conclude, "not to remain content with making superficial associations between terms, but to probe into the deeper meaning of the concepts employed by the Talmud."
The essay that follows illustrates how the Rebbe probes into the abstract meaning of Talmudic constructs, going beyond the surface and understanding the interplay of theoretical principles.
Moreover, these principles are not left in the abstract, but followed to their conclusion, giving us guidelines for our practice of Halachah.
May the study of the Rebbe's teachings lead to the era when "wisdom, knowledge, and truth will become abundant," with the coming of Mashiach.  And then we will merit fulfillment of the prophecy,  "And those who repose in the dust will arise and sing. "
Sichos In English
Pesach Sheni, 5755
Is a Breach Irreparable?
We are commanded:  "You shall count... seven perfect weeks."
There are sages of the post-Talmudic era  who interpret this charge as implying that the seven weeks must be counted as a single continuum.
If a person fails to count one day, he no longer has the opportunity to fulfill the mitzvah and need not count the days which follow.
Other sages  differ and maintain that the failure to count one day does not disqualify a person, and he may - and should - continue counting on the following days.
Generally, it is explained  that the first opinion considers the entire Counting of the Omer as one single mitzvah. Hence, the failure to count one day prevents one from continuing to fulfill the mitzvah.
The second opinion, by contrast, maintains that counting each day is a separate mitzvah. Therefore, the fact that one did not fulfill the mitzvah one night does not prevent one from fulfilling the mitzvah on the nights which follow.
Because of this difference of opinion, the Shulchan Aruch  rules that - in deference to the opinion that every day is a separate mitzvah - if one fails to count one day, one should continue counting on the days which follow. Nevertheless - in deference to the opinion that in such an instance a person can no longer fulfill the mitzvah - the Shulchan Aruch rules that one should not recite a blessing before counting. For according to that opinion, the person would be reciting the blessing in vain.
A New Conception of the Mitzvah
Several questions are raised with regard to the opinion that the Counting of the Omer is considered as one single mitzvah.
(These questions also apply with regard to the decision of the Shulchan Aruch.)
- If the entire Counting of the Omer is considered as one mitzvah, why do we recite a blessing every night before counting?
Seemingly, we should recite one blessing, either at the beginning of the counting or at its conclusion.
- Moreover, according to this opinion, it appears that just as missing the counting of one day prevents one from fulfilling the mitzvah in the future, it also has a retroactive effect and nullifies the counting of the previous days.
If so, how is it possible to recite a blessing before counting the Omer? There is the possibility that one will forget to count in the future and retroactively the blessing recited will be considered a blessing in vain.
These questions lead to the following conclusion:
The Counting of the Omer involves 49 mitzvos.
Therefore, a blessing is required every night, and there is no question regarding the retroactive disqualification of one's counting of the previous nights.
Nevertheless, if one fails to count the Omer one night, one can no longer count in the future.
Because the mitzvah is to count the days as a collective sum, for example, to count two or three days. And that is not possible if one has not counted the first or the second night.
Indeed, this concept is reflected in the wording used when counting the Omer: "one day...," "two days...," "three days...," i.e., a number that includes the previous days, rather than "the first day," "the second day," "the third day." For every day includes the previous days. 
Changes In Status
Among the ramifications of the above discussion is the following question: 
When a child becomes Bar Mitzvah, a servant is freed, or a person converts during the Counting of the Omer, may they recite a blessing when counting the remaining days of the Omer or not?
Before this change in their status, these individuals were not obligated to fulfill this mitzvah.
According to the opinion that each night is a separate mitzvah, they should count the Omer on the subsequent nights to fulfill the mitzvah incumbent upon them that night.
But according to the opinion that the entire counting is one mitzvah, they will never be able to fulfill the mitzvah. Since they were not obligated to count the first days, it is impossible for them to count the entire Omer.
In deference to the first opinion, they should count the Omer in the subsequent days. But seemingly, in deference to the second opinion, a blessing should not be recited.
With regard to a convert, it appears that there is no need for further consideration of the matter. The status attained by a convert is entirely new, as our Sages comment:  "A convert is like a new-born baby." From the time he attains this status, he begins a new leaf. As such, when he converts in the midst of the Counting of the Omer, even if he counted beforehand, there is no connection between his previous counting and his counting as a Jew. Hence, his Counting of the Omer cannot be "perfect. "
With regard to a servant and a minor, however, there is room for discussion.
Our Sages obligated a minor in the mitzvah of chinuch, that he be trained in the observance of the mitzvos. Included in the scope of this mitzvah is the Counting of the Omer.
Similarly, a servant may fulfill mitzvos even though he is not obligated to.
Thus questions arise:
When a child or a servant has counted the Omer before becoming fully obligated to do so, is that counting significant? Can he continue counting the Omer with a blessing in the subsequent days on this basis?
Differences Between the Counting of a Minor and the Counting of a Servant
Insight into the resolution of the above questions can be gained on the basis of the following theoretical discussion regarding the mitzvos that involve counting, e.g., the Counting of the Omer, and the Counting of the Shemitah and Yovel years.
Is the counting of these days or years significant in its own right? Or is the importance of the counting endowed to it by virtue of the mitzvah involved?
To apply this concept with regard to the counting of the Omer by a servant:
Do we say that the counting itself is significant, and thus when a servant has counted before he was freed, he may continue counting with a blessing? Or do we say that it is the mitzvah which endows the counting with significance, and the servant was not obligated to count before he was freed, the fact that he did count is of no consequence and his weeks cannot be "perfect"?
There is, moreover, a logical basis for the second opinion, for the passage of time is a factor regardless of whether a person marks its passage or not. What makes a person's taking notice of the passage of time unique and distinct? The fact that he is counting as a result of a Divine commandment and not on his own initiative.
With regard to a minor, it is possible to explain that since the minor was obligated to count because of the mitzvah of chinuch, that obligation confers a measure of significance to the days he counted as a minor. For this counting involves not merely the marking of the days as does the counting of a servant, but also the fulfillment of an obligation. Therefore, he can continue to count with a blessing in the days that follow.
(This interpretation depends on the explanation given above that even the approach which sees the Counting of the Omer as one continuum conceives of the counting of each night as a mitzvah, but requires that the counting be comprehensive, including all the previous days.
For it is obvious that the counting of the minor after the attainment of majority is of a different nature than his counting before he attains majority, and the two cannot be considered as elements of a single mitzvah.
When, however, we operate under the conception that every night is a separate mitzvah, but the counting must continue in an unbroken sequence, it is possible to posit that the minor's counting before attaining majority will enable him to continue counting with a blessing afterwards.)
Differences Between Rabbinic and Scriptural Commandments
This conclusion is not, however, a logical imperative.
For the mitzvah of chinuch is not incumbent on the minor himself. Instead, "a minor is not obligated to observe any of the mitzvos.... His father is obligated to train him in their observance... on the basis of a Rabbinical commandment." 
Moreover, there is a fundamental distinction between Scriptural commandments and Rabbinic commandments.
A Scriptural commandment may effect the gavra, the person observing the commandment - a person is obligated to perform or refrain from a particular activity, and/or the cheftza, the object or time span in which the commandment is observed - the object itself becomes forbidden or the timespan becomes consecrated.
According to many opinions,  a Rabbinic commandment is incumbent only the gavra, i.e., our Sages did not have the power to cause an object itself to be forbidden, they could only prohibit a person from using it. 
According to this distinction, it is possible to say that the Rabbinic obligation incumbent on the minor's father does not endow the days counted by the minor with enough significance for them to be considered as part of a single continuum with the days he will count after attaining majority. 
The Command Itself Endows Importance
There is, however, a deeper conception of the principle that the mitzvah endows an object with significance.
On this basis, one can postulate that when either a servant or a minor becomes obligated in the Counting of the Omer in the midst of the Omer, they may continue counting with a blessing if they counted beforehand.
The concept that a mitzvah endows the object with which the mitzvah must be observed with significance applies even before the mitzvah is actually observed.
To speak in metaphysical terms, there is no entity in this material world which has any significance in its own right in relation to G-d, as it is said,  "Before Him, everything is of no importance."
When can a material entity gain a certain measure of importance? When G-d commands that the entity be used in the observance of a mitzvah. With the command itself, the entity becomes significant. 
Based on this explanation, it is possible to say that the mitzvah of the Counting of the Omer itself endows the days with significance.
And therefore, when a minor or a servant counted these days despite the fact that he was not obligated by a Scriptural commandment, he can continue counting with a blessing. The days are considered part of a single continuum, because of G-d's command. 
Reaching the Ultimate Status
Our Rabbis explain that in the present era, the Counting of the Omer is not considered a mitzvah as mandated by Scriptural law.
It is only when the Beis HaMikdash will be rebuilt and we offer the Omer sacrifice and the two loaves brought on Shavuos that the counting will again enjoy the status of a Scriptural commandment. 
This is alluded to in the prayer we recite together with the Counting of the Omer:  "May the Merciful One restore the Beis HaMikdash to its place, speedily in our days." As the Alter Rebbe explains:  "The only reason which we count in the present era is to commemorate [the practice of] the Beis HaMikdash.... Therefore, we pray that the Beis HaMikdash be speedily rebuilt, and then we will be able to fulfill the mitzvah in its proper manner."
The simple meaning is that we are praying that Mashiach will come so that next year, we will be able to fulfill the counting of the Omer in a full and complete manner.
Based on the above, and based on our anticipation that Mashiach come in the most immediate future, it can be explained that the prayer expresses our wish that Mashiach come now, and then we will continue counting the Omer this year in fulfillment of a Scriptural commandment. 
For, like a child who has attained maturity in the midst of the Counting of the Omer, our counting before Mashiach's coming will be considered significant, and will enable us to continue fulfilling the mitzvah in the most complete manner, together with Mashiach in the Beis HaMikdash.
May this come to pass in the immediate future.
Adapted from Likkutei Sichos, Vol. I, p. 270; Vol. VIII, p. 54-55; Likkutei Sichos, Chag HaShavuos, 5751
1. Rambam, Mishneh Torah, Hilchos Teshuvah 9:2.
2. Yeshayahu 26:19.
3. Vayikra 23:15.
4. Halachos Gedolos.
5. Maharitz Chayot, in the name of Rav Hai Gaon.
6. See Shulchan Aruch HaRav 489 et al.
7. Shulchan Aruch, Orach Chayim 489:8.
8. Shibolei Leket, sec. 234; Pri Megadim, Eshel Avraham 489:13.
9. See Likkutei Sichos, Vol. III, p. 996, which explains the spiritual dimensions of this concept.
10. See Minchas Chinuch, Mitzvah 306; Tziyunim LaTorah, Principle 12, et al.
11. Yevamos 22a.
12. Shulchan Aruch HaRav, Hilchos Talmud Torah 1:1. See Likkutei Sichos, Vol. XVII, p. 232ff, where this subject is discussed.
13. See the Responsa entitled Tzafnas Paneach, Responsum 33; Mefaneach Tzufunos, Kuntres Meah Savaros; Asvan D'Oraisa, sec. 10, et al. See Sichos Acharon Shel Pesach, 5736, where this concept is discussed.
14. See, however, Tanya, ch. 8, which states that even foods which are forbidden by Rabbinic decree derive their nurture from the three impure kelipos, indicating - in contrast to the opinion stated above - that a Rabbinic commandment has the power to cause an object itself to be considered as forbidden.
15. Even according to the opinion, to be explained, that in the present era even the counting of the Omer by an adult merely fulfills a Rabbinic commandment, it is still possible to make the above distinction. For there is a distinction between a Rabbinic commandment of a primary nature (chad diRabbanan, i.e., a decree which the Sages required of an adult) and a secondary Rabbinic commandment of a secondary nature (trei diRabbanan, the obligation the Rabbis placed on a child to fulfill other Rabbinic commandments). See Shulchan Aruch HaRav 186:3 where this subject is discussed.
16. Zohar, Vol. I, p. 11b.
17. See Likkutei Sichos, Vol. XVI, p. 215; Vol. VII, p. 32 which explains related concepts.
Needless to say, the fulfillment of the command endows the article with a lasting dimension of holiness which did not exist previously. But independent of whether the command is observed or not, the very fact that it was issued grants the entity with which it is performed importance.
18. The person must, nevertheless, do his part in echoing this Divine initiative. Therefore, if he fails to count one of the days of the Omer, he has broken the continuum, and can no longer count with a blessing.
The above concepts do not apply to a convert. He may not recite a blessing even though he counted the days of the Omer before he converted. Since conversion causes him to become a totally new entity, "a new child" as it were, there is no connection between his counting of the Omer before conversion and his subsequent counting. The two periods of time cannot be considered a single continuum at all.
19. Shulchan Aruch HaRav 489:2.
20. Siddur Tehillat HaShem, p. 341.
21. Shulchan Aruch HaRav 489:11.
22. One might raise a difficulty: As evident from the Shulchan Aruch HaRav 489:2, the Counting of the Omer attains the status of a Scriptural commandment only after the Omer has been offered. If Mashiach will come in the midst of the Omer, the Omer itself will not have been offered, and hence the counting will not have the status of a Scriptural mitzvah. This difficulty can be resolved as follows: When describing the Counting of the Omer, the Torah (Vayikra 23:15) states: "You shall count seven weeks from the day after the day of rest, [i.e., the Pesach holiday,] when you brought the omer as a wave offering until the day after the seventh week... when you will bring new grain as a meal offering...." The Torah associates the counting with both the omer offering and the two loaves of grain on Shavuos. Thus even if the omer offering was not brought on the sixteenth of Nissan, the counting can still be considered a Scriptural commandment because of the connection to Shavuos. See the Responsa of the Radbaz, Responsum 1327. Note sources quoted in Likkutei Sichos, Chag HaShavuos, 5751, footnote 17 and 35.