It is written in the Haggadah of Pesach that we will continue to mention the redemption from Egypt even in the days of Moshiach. Why?
The character of the final redemption will be different from the character of the redemption from Egypt. After the Jews were redeemed from Egypt, much evil remained in the world, but was subdued for the moment. The powers of holiness, of good, overpowered the forces of evil, and the Jews were released from Egypt. On the other hand, with the final redemption evil will be eradicated completely. Impurity will cease to exist and only holiness and good will remain.
The ideal state is when no evil at all remains. Then we will serve G-d completely with no distractions or disturbances. As long as evil remains, even if it is subjugated, it can be awakened at any time. In that case, however, why will we continue to mention the exodus from Egypt even after the complete redemption will come? Won’t the previous redemption be completely nullified in comparison?
However, in the “lower” state there is an advantage over the higher state of the final redemption. When a person does not need to contend with constant challenges or difficulties, and life runs smoothly, his life does not reflect his complete dedication to G-d. Observance comes easily to him and fits in with his lifestyle. He lacks the quality of kabbalat ol, acceptance of Divine authority. This quality can be found only when one must overcome hardships to serve G-d.
In a practical sense, the ultimate redemption will also have the benefits of the redemption from Egypt. The teachings of Chassidut expand on the concept that even though the forces of impurity will be eradicated, we will still have the quality of kabbalat ol. Therefore, we will continue to mention the exodus from Egypt even after the final redemption, even though it will be secondary to the ultimate redemption.
(Sefer Hamaamarim Melukat, vol. 2, p. 37. Likutei Sichot vol. 17, p. 125.)