en_tn_lite_do_not_use/rev/21/27.md

nothing unclean will ever enter into it, nor anyone

This can be stated in positive form. AT: "only what is clean will ever enter, and never anyone" (See: rc://en/ta/man/translate/figs-doublenegatives)

but only those whose names are written in the Lamb's Book of Life

This can be stated in active form. AT: "but only those whose names the Lamb wrote in his Book of Life" (See: rc://en/ta/man/translate/figs-activepassive)

the Lamb

This is a young sheep. Here is it used symbolically to refer to Christ. See how you translated this in Revelation 5:6. (See: rc://en/ta/man/translate/writing-symlanguage)