John Gill Commentary Lamentations 2:17

"Jehovah hath done that which he purposed; he hath fulfilled his word that he commanded in the days of old; He hath thrown down, and hath not pitied: And he hath caused the enemy to rejoice over thee; he hath exalted the horn of thine adversaries." — Lamentations 2:17 (ASV)

The Lord has done [that] which he had devised It was not so much the Chaldeans that did it, though they ascribed it to themselves; but it was the Lord's doing, and what he had deliberately thought of, purposed and designed within himself; all whose purposes and devices certainly come to pass.

he has fulfilled his word that he had commanded in the days of old; not only by the mouth of Jeremiah, years ago, or in the times of Isaiah, long before him; but even in the days of Moses; see (Leviticus 26:17) , &c. (Deuteronomy 28:20) So the Targum, "which he commanded to Moses the prophet from ancient days, that if the children of Israel would not keep the commands of the Lord, he would take vengeance on them:"

he has thrown down, and has not pitied; he has thrown down, or caused to be thrown down, without any pity, the walls of Jerusalem; and not only the houses and palaces in it, but also his own house, the temple.

and he has caused [your] enemy to rejoice over you; giving them victory, and putting all into their hands; on which they insulted them, and gloried over them.

he has set up the horn of your adversaries; increased their strength and power, their kingdom and authority; and which swelled their pride, and made them more haughty and insolent.