Thomas Aquinas Commentary Lamentations 4:15

"Depart ye, they cried unto them, Unclean! depart, depart, touch not! When they fled away and wandered, men said among the nations, They shall no more sojourn [here]." — Lamentations 4:15 (ASV)

Here he presents the mockery of their enemies against the captive citizens.

1. He reproaches them for the profanation of the holy places: they cried out—that is, their enemies—to them—that is, the Jews; depart from the holy place into captivity; touch not the sacred things, you who are impure. Whoever of the seed of Aaron the priest has a blemish, he shall not approach to offer sacrifices to the Lord (Leviticus 21:21).
2. He reproaches them for God’s indignation, shown by the loss of divine help: they quarreled—that is, their enemies against the Jews; and being removed from each other, some by quarreling and others by sorrowing; he will no more dwell, meaning God will no longer defend you. Saying: God has forsaken him (Psalms 71:11).