Thematic Bible: No entrance into heaven without cleansing

And one of the elders answered, saying to me, "These who are clothed in white robes, who are they, and whence did they come?" And I have said to him, "My lord, you know." And he said to me, "These are those who come out of the great tribulation; and they washed their robes, and made them white in the blood of the Lamb.