One of the elders explained to John about the saints who are dressed in white robes.

Revelation 7:13-17

13 Then one of the elders asked me, “These people who are wearing white robes, do you know who they are, and where they come from?” 14 I answered him, “Sir, I do not know. Surely you know who they are!” He said to me, “These are the people ◄whom others have caused to suffer greatly/who have been persecuted►. Because they believed that Jesus, the one who is like a sacrificial lamb, atoned for our sin when his blood flowed from his body when he died, it is as though [MET] they have washed their robes and have made them clean and white. 15 Because of this, they are in front of God’s throne, and they serve him day and night in his heavenly temple. God, the one who sits on the throne, will shelter/protect them [MTY]. 16 As a result, they will never again be hungry. They will never again be thirsty. The sun will never again ◄beat on/burn► them, nor will any heat scorch them. 17 This is because the one who is like a lamb who is at the throne will take care of them, just like a shepherd takes care of his sheep [MET]. He will guide them to the source of eternal life, just like a shepherd leads his sheep to springs of water, which enable the sheep to live [MET]. God will cause them to no longer be sad. It will be as if he were wiping away all tears from their eyes [MTY].”