John Gill Commentary Lamentations 3:12

"He hath bent his bow, and set me as a mark for the arrow." — Lamentations 3:12 (ASV)

He has bent his bow
Which is put for all the instruments, of war; the Chaldeans were archers, and shot their arrows into the city:

and set me as a mark for the arrow ;
as a target to shoot at; signifying that God dealt with him, or his people, as enemies, the object of his wrath and indignation; and if he directed his arrow against them, it must needs hit them; there was no escaping his vengeance; see (Job 7:20) (16:12) .