Thomas Aquinas Commentary Lamentations 2:18

"Their heart cried unto the Lord: O wall of the daughter of Zion, let tears run down like a river day and night; Give thyself no respite; let not the apple of thine eye cease." — Lamentations 2:18 (ASV)

Here the prophet turns to imploring the Judge's mercy through prayer.

He begins by outlining two main actions. First, he calls the people to prayer. Second, he presents the prayer itself, beginning with Behold, O LORD, and consider (Lamentations 2:20).

Regarding the call to prayer, he does two things. First, he teaches that the way to prayer should be prepared with tears. Second, he teaches how to pray, beginning with the words Arise, praise God (Lamentations 2:19).

Concerning the first of these points—preparing with tears—he makes three arguments.

First, he presents the reason for mourning. The phrase their heart can refer to the heart of their enemies. They cried out in blasphemy to the Lord—that is, against Him—from upon the walls. They acted as if the city's destruction was an opportunity for blasphemy, suggesting that God had been unable to defend it. As Scripture says, Your murmuring is not against us, but against the LORD (Exodus 16:8).

Alternatively, their heart refers to the heart of the Jews, teaching them to express their heart's sorrow in tearful prayer. As the psalmist says, I cried with my whole heart; hear me, O LORD (Psalms 119:145).

Second, he calls them to shed an abundance of tears: let tears run down like a torrent. As Jeremiah says elsewhere, Let our eyes shed tears, and our eyelids run down with waters (Jeremiah 9:18).

Third, he calls them to mourn continuously, day and night. This means in both prosperity and adversity, or it could be taken literally to mean at all times, whether actively or habitually. As the prophet says, Let my eyes shed down tears night and day (Jeremiah 14:17).