See vanity unto thee. — “See” is used in the sense of the utterances of the “seer,” or prophet. The Ammonites also had false prophets among them.
Thee upon the necks of them that are slain. — Judah is to fall first, then Ammon immediately after, as it were, upon the necks of those already slain. The figure is taken from the battle, in which one warrior falls upon the body of him who fell before him.
When their iniquity shall have an end. — Not through repentance, but because it ceases of necessity with the death of the sinner.