Gemara Sanhedrin 97b: Moshiach comes only when we do teshuvah. R’ Eliezer and R’ Yehoshua argue how that happens — on our own, or because Hashem forces it — but both agree it has to happen first.

Rambam Rules: Teshuva must precede redemption. Torah promises, Yidden will do Teshuva by the end of exile and be immediately redeemed! Hilchos Teshuva 7:5

Moshiach Makes it Happen: Even before he is fully revealed, Moshiach fixes the world and arouses all Yidden to do teshuvah. He is the one who brings about the very teshuvah that the Torah promises and that brings the redemption. Hilchos Melachim 11:4

How it Fits: The redemption depends on teshuvah. The Torah guarantees that teshuvah will happen. Moshiach is the shliach who causes that guaranteed teshuvah, which then brings immediate geulah.

The Rebbe testifies outright: the full measure of teshuva required to bring Geula has already been done by every single Jew. Just thinking about doing teshuva — even for a moment in your mind — was enough.

And anyone not doing Torah and mitzvos right now is completely forced by circumstances beyond their control. So when they do even one mitzvah, it’s infinitely precious to Hashem.

Which means: we don’t need to do any more teshuva to bring Geula. The work is done. Moshiach can come this instant.

(Sefer Hasichos 1:232 5751, Hisvadiyus 3:1232 5743, Hisvadiyus 1:249 5752)