17 The LORD hath done that which he had devised; he hath fulfilled his word that he had commanded in the days of old: he hath thrown down, and hath not pitied: and he hath caused thine enemy to rejoice over thee, he hath set up the horn of thine adversaries.
[AD 1274] Thomas Aquinas on Lamentations 2:17
Second, is shown what is true in words. As: "he carried out his threat". For, the Lord God prescribed destruction of his people: "as he ordained long ago" (cf Deuteronomy, Chapter 28: "Consequences of Disobedience").
Or, such is even exposed by the very first prophets. As said in Numbers 23:19: "Has he said, and will not do it? Or has he spoken, and will he not fulfil it?"
Then, the condemnation itself is indeed shown. So Verse 17 ends: "he has demolished without pity, he has made the enemy rejoice over you and exalted the might of your foes". For, Psalm 89:43 declares: "and thou hast not made him stand in battle."