The voice John hears is “another” voice, in contrast to the angel who had just spoken, Revelation 18:1–3. Whereas the earlier speaker (an angel) had come down from heaven (and so spoke on earth), the present speaker does his speaking “from heaven.” In Revelation 4—16 John had himself been in heaven and witnessed much of what was happening there, including the throne of God and the Lamb, the living creatures around the throne, and the angels who do the Lord’s bidding. The present voice comes from that place. We are not told who the speaker is (and so we should not speculate as to whether this is an angel or the Lamb or even God himself). It is enough to know that the voice comes from heaven, that is, from creation’s headquarters where Christ is enthroned (Revelation 5:1–14) and where Satan and darkness and evil cannot muffle or distort clear instruction (Revelation 12:9).
4 Then I heard another voice from heaven saying, “Come out of her, my people, lest you take part in her sins, lest you share in her plagues;