True Redemption Includes Every Single Jew

"The inner meaning of the redemption is—the revelation of the essential bond (קשר העצמי) that exists between Bnei Yisroel and the Holy One, blessed be He. If even one Jew remains in exile, then this indicates that the redemption is not true. The future redemption is called 'the true and complete redemption' and thus it will be the redemption of all Yisroel."

Sicha of the Lubavitcher Rebbe, 5748 (free translation)