Charles Ellicott Commentary Revelation 21:27

"and there shall in no wise enter into it anything unclean, or he that maketh an abomination and a lie: but only they that are written in the Lamb`s book of life." — Revelation 21:27 (ASV)

And there shall in no wise enter into . . .—Better, And there shall never enter into her anything unclean, and he that worketh abomination and falsehood, but only (or, except) they that have been written in the book of life of the Lamb.

The gates stand open always, but no evil thing may find a home there. The emphatic repetition here of the idea that all sin is excluded, is in harmony with all other Scripture: no unholiness can dwell in the presence of God. The allusion is to the care of the Jews to exclude all things unclean from the precincts of the sanctuary. The legal and ceremonial defilement had its spiritual significance, which the Apostles utilized elsewhere. (Compare 2 Corinthians 6:17–18; 2 Corinthians 7:1; Revelation 18:4. On the “book of life,” see Revelation 20:12.)