Revelation 7:9-10 After these things (144K Sealed), I looked, and behold, a great multitude which no one could number, of all nations, tribes, peoples, and tongues, standing before the throne and before the Lamb, clothed with white robes, with palm branches in their hands, and crying out with a loud voice, saying,“Salvation belongs to our God who sits on the throne, and to the Lamb!”

Who are they?

Revelation 7:13-17 Then one of the elders answered, saying to me, “Who are these arrayed in white robes, and where did they come from?” I said to him, “Sir, you know.” So he said to me, “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. Therefore they are before the throne of God, and serve Him day and night in His temple. And He who sits on the throne will dwell among them. They shall neither hunger anymore nor thirst anymore; the sun shall not strike them, nor any heat; for the Lamb who is in the midst of the throne will shepherd them and lead them to living fountains of waters. God will wipe away every tear from their eyes.”

Revelation 19:1-6 After these things I heard a loud voice of a great multitude in heaven, saying, “Alleluia! Salvation and glory and honor and power belong to the Lord our God! ² For true and righteous are His judgments, because He has judged the great harlot who corrupted the earth with her fornication; and He has avenged on her the blood of His servants shed by her.” Again they said, “Alleluia! Her smoke rises up forever and ever!” ⁴ And the twenty-four elders and the four living creatures fell down and worshiped God who sat on the throne, saying, “Amen! Alleluia!” Then a voice came from the throne, saying, “Praise our God, all you His servants and those who fear Him, both small and great!”

Revelation 19:6-9 I heard, as it were, the voice of a great multitude, as the sound of many waters and as the sound of mighty thunderings, saying, “Alleluia! For the Lord God Omnipotent reigns! Let us be glad and rejoice and give Him glory, for the marriage of the Lamb has come, and His wife has made herself ready.” And to her it was granted to be arrayed in fine linen, clean and bright, for the fine linen is the righteous acts of the saints. Then he said to me, “Write: ‘Blessed are those who are called to the marriage supper of the Lamb!’” And he said to me, “These are the true sayings of God.”