But outside are dogs
Dogs is κύνες [kynes] which refers to those who are impure, as an unclean animal1 (Ps. Ps. 22:16, Ps. 22:20; Isa. Isa. 56:10-11; Mtt. Mat. 7:15; Php. Php. 3:2).
The dogs . . . is a metaphor for the morally impure as it is throughout Scripture. They represent male prostitutes (Deu. Deu. 23:18), Gentiles (Mtt. Mat. 15:26), and Judaizers (Php. Php. 3:2-3), among other things (cf. 2K. 2K. 8:13; Ps. Ps. 22:16, Ps. 22:20; Isa. Isa. 56:10; Mtt. Mat. 7:6; Mark Mark 7:27). In the Orient dogs are scavengers and are objects of great contempt.2sorcerers . . . sexually immoral . . . murderers . . . idolaters . . . whoever loves and practices a lie
Whoever loves and practices a lie is πα῀ς φιλῶν καὶ ποιῶν ψεῦδος [pas philōn kai poiōn pseudos] : all while continually loving and continually doing [a] lie. See commentary on Revelation 21:8.
Sorcerers is οἱ φάρμακοι [hoi pharmakoi] : those who use drugs for magical arts. See commentary on Revelation 9:21.
Sexually immoral is οἱ πόρνοι [hoi pornoi] : a prostitute or fornicator. The same root word as Harlot.
The verse does not intend to teach that in the eternal state all manner of wicked men will be living just outside the heavenly city. It simply describes the future with the imagery of the present. The contrast is between the blessedness of the faithful and the fate of the wicked.3
1 Frederick William Danker and Walter Bauer, A Greek-English Lexicon of the New Testament and Other Early Christian Literature (Chicago, IL: University of Chicago Press, 2000), 461.
2 Robert L. Thomas, Revelation 8-22 (Chicago, IL: Moody Press, 1995), Rev. 22:15.
3 Robert H. Mounce, The Book of Revelation (Grand Rapids, MI: William B. Eerdmans Publishing Co., 1977), Rev. 22:15.