Would we have merited the ultimate Redemption had we never gone down into exile?
The Alter Rebbe, Rabbi Schneur Zalmen of Liadi, writes: “The ultimate perfection of the days of Moshiach and the resurrection of the dead… depends on our actions and service during the course of exile.” In other words, the ultimate Redemption depends on our Divine service during exile.
This raises the question: During the time that the Holy Temple stood in Jerusalem, it was possible to perform many more mitzvoth than we can today. Logic would say that the more mitzvoth we fulfill, the more we hasten the Redemption.
The explanation is based on the prophecy of Isaiah: “And the glory of G-d will be revealed, and all flesh together will see that the Name of G-d has spoken” (40:5). The Redemption is a time when the physicality of the world itself, the “flesh,” will recognize the glory of G-d. The same physical substance that today conceals the presence of G-d will be transformed and become unified with G-d. As the teachings of Chassidus explain, “Even animals will recognize their Creator” (Toras Chaim, Tetzaveh, 482:1).
In order for the physicality of the world to reach this state, there must first be a condition in which it takes an active role in revealing G-dliness in this world. If not, then when Moshiach comes the physicality of this world will have no relationship at all to holiness and will not be changed at all. It will not conceal or disturb the revelation of G-dliness, but it will not in itself be connected. The flesh will not conceal G-d, but it will not recognize Him either.
This is the advantage of the period of exile compared to the time of the Holy Temple. The difficulties of exile arouse in the Jews the power of Mesirus Nefesh—to overcome all challenges. This self-sacrifice draws down a lofty level of Divine light. The thick spiritual darkness that reigns in exile serves as a force which actually increases the power of the spiritual. Therefore, after exile we will reach a level in which the physical will join completely with the spiritual.
Tanya, Chapter 37. Likutei Sichos vol. 17, p. 93