The Great Multitude is one of two groups (along with the 144,000) who are presented to answer the question at the end of chapter 6, “The great day of His (God’s) wrath has come, and who is able to stand?” (Revelation 6:17). In other words, these are people who remain faithful to God during the stress of the Time of Trouble. There has been quite a bit of confusion regarding the relationship between the 144,000 and the Great Multitude.
First of all, both groups appear at the very end of time. The 144,000 give their message during “the hour of (God’s) judgment” (Revelation14:1-7) and the Great Multitude “are the ones who come out of the great tribulation” (Revelation 7:14). The “Great Tribulation” takes place just before the time when “(God’s) people shall be delivered” and “many of those who sleep in the dust of the earth shall awake” (Daniel 12:1,2), in other words, just before the Second Coming of Christ.
But there is a distinction between the two groups. In contrast to the 144,000, who are sealed out of “all the tribes of the (spiritual) children of Israel” (Revelation 7:4), the Great Multitude is “of all nations, tribes, peoples and tongues” (Revelation7:9). Moreover, in chapter 14 we learn that the 144,000 are “Virgins”, in other words, they have not committed spiritual adultery by participating in idolatrous worship (this does not mean that they are sinless, just that they have not worshipped other gods).
In contrast, the Great Multitude, even though God calls them “My people”, are in Babylon, the “Great Harlot” of the time of the end,— God sends a message to them, “Come out of her my people” (Revelation 18:4).
There are two groups of people who belong to God at the end of time: those who, in ignorance, have ended up in “Babylon” (the false politico-religious system of the last days), who need to come out of her in order to be saved, and those who have never been in Babylon (the 144,000) who give God’s message to come out of Babylon. This theme of God’s special messengers who call the multitudes out of Babylon is the focus of chapters 10 and 11 (the ministry of the Two Witnesses) and chapter 14 (the messages of the Three Angels).
When the Great Multitude responds to the call to leave Babylon they join the 144,000 so that there is no longer a distinction between the two groups. Although they are in the midst of the most traumatic period of earth’s history (the Great Tribulation), they are so close to God that the boundary between heaven and earth seems to dissolve; and by faith they are standing “before the throne” on the “sea of glass” (Revelation 7:14,15, 15:2) while all around them the “Seven Last Plagues” are falling on the “wicked” who have been trying to destroy them.
There is a lot more scriptural support and information about the 144,000 and the Great Multitude in chapters 7, 10, 11 and 14 of The Book.