Question:

Is it true that Moshiach will come only after all souls that are destined to be born have descended to the world?

Answer:

Our sages say: “The son of David will not come until all souls in [the heavenly treasury called] Guf will be emptied. In the Midrash Tana D’vei Eliyahu it is written that the final Redemption will be similar to the redemption from Egypt: “Just as the Jews were redeemed from Egypt in merit of their fruitfulness, so will they be redeemed in the future in merit of their being fruitful, and they will fill the entire earth.”

The Lubavitcher Rebbe explains that the words of our sages have a dual meaning. On the surface, the knowledge that the birth of each child hastens the Redemption gives greater urgency and desire to fulfill the mitzvah of being fruitful and multiplying.

On a deeper level, the mitzvah of being fruitful does not only apply to giving birth to physical children, but also to drawing Jews closer to their spiritual roots. When a Jew discovers the path of Torah and mitzvot and begins to follow it, it is as if he is reborn. It is understood that once all the souls find their way back to Torah, Moshiach will come.

This gives an additional meaning to the words of Maimonides, who writes: “One who adds a single soul to Israel is as if he built a world.” In addition to its plain meaning, referring to the birth of a Jewish child, we can also interpret this statement as one who draws a Jewish soul closer to Judaism. Through this, it is as if he built a world. He is doing his part to bring the world to its ultimate state of perfection, which we will experience in the time of Redemption.

(Yevamos 62a, see Rashi. Tana D’vei Eliyahu Zuta, chapter 14. Mishnah Torah Hilchos Ishus, 15:16. Shnei Luchos Habris, Bereishis. Likutei Sichos vol. 25 p. 37, and vol. 30, p. 30.)