“And he [the elder] said to me: ‘These are the ones that come out of the great tribulation, and they have washed their robes and made them white in the blood of the Lamb.

Revelation 7:14b,

23. What is the great tribulation from which the great crowd “come out”?

²³ On an earlier occasion, Jesus had said that his presence in Kingdom glory would culminate in “great tribulation such as has not occurred since the world’s beginning until now, no, nor will occur again.” (Matthew 24:21, 22) In fulfillment of that prophecy, the angels will unleash the four winds of the earth to devastate Satan’s world system. First to go will be Babylon the Great, the world empire of false religion. Then, at the peak of the tribulation, Jesus will deliver the remaining ones of the 144,000 on earth, together with the multitudinous great crowd.​—Revelation 7:1; 18:2.