A.T. Robertson Commentary Revelation 18:4

"And I heard another voice from heaven, saying, Come forth, my people, out of her, that ye have no fellowship with her sins, and that ye receive not of her plagues:" — Revelation 18:4 (ASV)

Come forth, my people, out of her (εξελθατε, ο λαος μου, εξ αυτης). Second aorist (urgency) active imperative (-α form) of εξερχομα. Like Isa 48:20; 52:11; Jeremiah 50:8; 51:6, (about Babylon). See also the call of Abram (Genesis 12:1). the rescue of Lot (Genesis 19:12ff.). In the N.T. see Mr 13:4; 2 Corinthians 6:14; Ephesians 5:11; 1 Timothy 5:11. Hο λαος is vocative with the form of the nominative.

That ye have no fellowship with her sins (ινα μη συνκοινωνησητε ταις αμαρταις αυτης). Purpose clause with ινα μη and the first aorist active subjunctive of συνκοινωνεω, old compound (συν, together, κοινωνος, partner), in N.T. only here, Php 4:14; Ephesians 5:11. With associative instrumental case αμαρτιαις.

And that ye receive not of her plagues (κα εκ των πληγων αυτης ινα μη λαβητε). Another purpose clause dependent on the preceding, with ινα μη and the second aorist active subjunctive of λαμβανω, and with proleptic emphatic position of εκ των πληγων αυτης before ινα μη.