Actually, this is false.
During the Tribulation there will be 144,000 Messianic Jews on Earth who will have been converted by God to Christianity. These are known as the "Tribulation Saints," whose sole purpose is to save as many as possible
after the Rapture.
Revelation tells us that, when those saved by these Saints stand before God, their number is too large to count. These will be people who did not believe in time to participate in the Rapture, but who knew their error once these last few Biblical prophecies became fulfilled, and who then convert to Salvation in Christ.
..."These are the ones who come out of the Great Tribulation, and washed their robes and made them white in the blood of the Lamb."