Her burning will be visible by her kings, merchants, and shipmasters who stand off at a distance (Rev. Rev. 18:10+, Rev. 18:15+, Rev. 18:17+).
The English word alas only partly conveys the feeling in the Greek ouai , the very sound of which bespeaks grief and terror. It is the same word translated woe elsewhere (as in Revelation Rev. 8:13+).1 Her luxurious wealth and position as a center of trade had made them rich, but now it was all gone (Rev. Rev. 18:16+, Rev. 18:19+). Their lamentation reflects their sorrow over the loss of their own self-interests rather than the city itself.
that great city Babylon, that mighty city!
The depth of her destruction is magnified by the height which she appeared to have attained prior to her fall. See commentary on Revelation 18:2.
For in one hour your judgment has come
The conjunction for, ὅτι [hoti] , indicates the reason for their outburst: her destruction was so sudden and complete. She had appeared to be so mighty, virtually unassailable, yet now she had been suddenly devastated and brought down to nothing. See Babylons Predicted Destruction.