Two Offerings: Water and Wine
Our Sages state  that "he who has not witnessed the celebration of Simchas Beis HaShoevah has never seen happiness in his life."
This refers to the celebration which accompanied the water libation, the offering of water in the Beis HaMikdash on Sukkos.
During this unique celebration, the Sages "would dance...with lighted torches, singing songs and praises, and the Levites would play harps and lyres, cymbals and trumpets, and countless other musical instruments." 
In many respects, the water offering paralleled the wine offering that accompanied both the daily sacrifices and the additional Mussaf sacrifices offered on the holidays.
In fact, the Torah's only allusion to the water offering appears in its description of the wine offering.  Nevertheless, no outstanding celebration marked any of the wine offerings, even though it is wine, not water, that figures prominently in the joy of so many festive occasions.
Paradoxically, the Jewish people's greatest outpouring of joy was associated with the water offering, not with wine.
Limited and Unlimited Happiness
Based on the principle that we must thank G-d for all the pleasure we experience in this world, our Sages instituted the blessings recited before eating or drinking. 
The Sages indicated the unique status of wine - the degree to which it gives pleasure - by composing a special blessing for it, "boreh pri hagafen."
In contrast, they did not regard water, which is tasteless, as sufficiently pleasure-inducing to warrant a blessing; only when a person drinks water to quench his thirst is a blessing required. 
Wine and water represent different approaches to our service of G-d.
The Hebrew word taam has two meanings, "taste" and "reason".
Taste and reason are related because the comprehension of an intellectual idea produces palpable satisfaction, not unlike the pleasure derived from tasting good food. 
Because wine is pleasant-tasting it has come to symbolize the kind of divine service that is flavored by understanding. 
Water, which is tasteless and simple, symbolizes kabbalas ol, the acceptance of the yoke of heaven - a simple commitment to fulfill G-d's will whether one understands or not.
Generally, we take pleasure from performing a mitzvah we understand, because this enables us to appreciate the positive effect produced by our efforts.
By the same token, when we do not understand the reasons for a mitzvah, we may feel less fulfilled. Though we may be willing to obey G-d's will at all times, we do not usually derive as much pleasure from mitzvos which require our unquestioning acceptance.
There are times, however, when the approach of kabbalas ol generates a satisfaction deeper and more fulfilling than that which is experienced from a rational service of G-d.
When we are "thirsty", when we desire to be united with G-d in a way that transcends the limited scope of our thoughts and feelings, we derive pleasure from "water", from kabbalas ol.
At this level of commitment, the pleasure of fulfilling mitzvos through kabbalas ol exceeds the satisfaction of the rational approach, since the happiness produced through our understanding is, by definition, limited in proportion to our understanding.
The more extensive our knowledge, the greater the pleasure we receive; where our knowledge is limited, so is our pleasure.
In contrast, the commitment of kabbalas ol that results from "thirst" results in a happiness that knows no bounds. For by making a commitment beyond the scope of our understanding, we connect with the infinite dimensions of G-dliness.
This brings about a joy which entirely surpasses our human potential.
In Continuation of the Days of Awe
In this context, Sukkos and the water offering can be seen as a stage in the progressive divine service begun on Rosh HaShanah.
On Rosh HaShanah and Yom Kippur we accept G-d's sovereignty and turn to Him in sincere teshuvah.
These days challenge us to penetrate to our core and awaken within ourselves a "thirst" to enter into a deep, all- encompassing relationship with G-d.
This "thirst" is satisfied through the service of kabbalas ol that is symbolized by the water offering.
The celebrations of Sukkos are an outgrowth of our soul-searching on Rosh HaShanah and Yom Kippur.
Because we awaken a commitment to G-d that is unlimited, our celebrations are likewise unbounded.
A Timeless Relationship
Both the wine offerings and the water offering had to be brought during the daytime.
However, while a wine offering offered at night was thereby invalidated, this restriction did not apply absolutely to the water offering; after the fact, it was acceptable even at night. 
Day and night are classic metaphors for states of revelation and concealment in our divine service.
A rational commitment, which is symbolized by the wine offering, is relevant only "during the day," when one has a conscious awareness of G-dliness.
Since a rational commitment fluctuates with the varying extent of each person's understanding, it grows weaker when one's awareness wanes. A commitment based on kabbalas ol, by contrast, weathers all seasons; it is not shaken, even when our understanding is weak.
Fusing Both Approaches
The unique significance of the water offering does not minimize the importance of the wine offering; both were required in the Beis HaMikdash.
Similarly, in the personal sphere, each mode of divine service complements the other.
While the basis of our service of G-d must be kabbalas ol, that simple and superrational commitment is enhanced and intensified by a conscious relationship with G-d. A commitment to G-d which exists beyond the limits of our understanding is not sufficient.
For our relationship with G-d to be complete, it should be internalized until it permeates and involves all of our faculties - and that includes our minds.
The Key to Happiness
Sukkos is "the time of our rejoicing," a week-long celebration that includes an entire cycle of time and influences all the weeks that follow, infusing joy and pleasure into every aspect of our service of G-d.
Though the Beis HaMikdash is destroyed, we can experience - at least in some measure - the happiness of Simchas Beis HaShoevah by commemorating the water offering with celebrations throughout the Sukkos holiday. Participating in these celebrations generates the potential for us to "see happiness" throughout the year to come.
This happiness will also include the ultimate celebrations of the Era of the Redemption. At that time the sacrificial service will be renewed, and with joyful hearts we will bring both the water and wine offerings in the Beis HaMikdash. May this take place in the immediate future.
Adapted from Likkutei Sichos, Vol. II, Sukkos
1. Sukkah 51b.
2. Op. cit., 51a.
3. Rashi on Bamidbar 29:18; Taanis 2b.
4. Berachos 35a; Rambam, Hilchos Berachos 2:1.
5. Berachos 44a.
6. See Kuntres Uma'ayon, Discourse 1.
7. See Likkutei Torah, Sukkos, p. 79d.
8. The Jerusalem Talmud, Tractate Sukkah 4:7.