Thematic Bible: No entrance into heaven without cleansing

And one of the elders answered, saying to me, "These who are dressed [in] the white robes--who are [they], and from where have they come?" And I said to him, "My lord, you know." And he said to me, "These are the ones who have come out of the great tribulation, and have washed their robes and made them white in the blood of the Lamb.