Revelation 7:13-15

13Then one of the elders asked me, “These dressed in long white robes – who are they and where have they come from?”

14So I said to him, “My lord, you know the answer.” Then he said to me, “These are the ones who have come out of the great tribulation. They have washed their robes and made them white in the blood of the Lamb!

15For this reason they are before the throne of God, and they serve him day and night in his temple, and the one seated on the throne will shelter them.