Jamieson, Fausset and Brown on Revelation 18:20

20. holy apostles--So C reads. But A, B, Vulgate, Syriac, Coptic, and Andreas read, "Ye saints and ye apostles."

avenged you on her--Greek, "judged your judgment on (literally, exacting it from) her." "There is more joy in heaven at the harlot's downfall than at that of the two beasts. For the most heinous of all sin is the sin of those who know God's word of grace, and keep it not. The worldliness of the Church is the most worldly of all worldliness. Hence, Babylon, in Revelation, has not only Israel's sins, but also the sins of the heathen; and John dwells longer on the abominations and judgments of the harlot than on those of the beast. The term 'harlot' describes the false Church's essential character. She retains her human shape as the woman, does not become a beast: she has the form of godliness, but denies its power. Her rightful lord and husband, Jehovah-Christ, and the joys and goods of His house, are no longer her all in all, but she runs after the visible and vain things of the world, in its manifold forms. The fullest form of her whoredom is, where the Church wishes to be itself a worldly power, uses politics and diplomacy, makes flesh her arm, uses unholy means for holy ends, spreads her dominion by sword or money, fascinates men by sensual ritualism, becomes 'mistress of ceremonies' to the dignitaries of the world, flatters prince or people, and like Israel, seeks the help of one world power against the danger threatening from another" [Auberlen]. Judgment, therefore, begins with the harlot, as in privileges the house of God.