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 (88): 43 declares: "and thou hast not made him stand in battle."
"Cry aloud to the Lord! O daughter of Zion! Let tears stream down like a torrent day and night! Give yourself no rest, your eyes no respite!"
Here one turns toward seeking divine justice through prayer. First, one is invited to pray, second to consider the prayer itself. As Verse 20 says: "Look, O Lord, and see! With whom hast thou dealt thus?"
Regarding an invitation to pray, two notions are proposed. First, one is taught to prepare a place for prayer through tears; second, one will be taught a manner of praying. As Verse 19 states: "Arise, cry out in the night, at the beginning of the watches."
Around the place prepared for prayer three ideas are set forth. First, the reason for wailing, or lementing is exposed. As said: "Cry aloud to the Lord! O daughter of Zion!" Namely, regarding enemies.