Charles Ellicott Commentary 2 Chronicles 20:3

"And Jehoshaphat feared, and set himself to seek unto Jehovah; and he proclaimed a fast throughout all Judah." — 2 Chronicles 20:3 (ASV)

And Jehoshaphat. — And he was afraid (namely, at the news). And Jehoshaphat set his face, etc. Literally, put his face—a phrase used in Daniel 9:3 (compare 2 Kings 12:18), and implying resolved, determined.

To seek the Lord. —The Hebrew construction is that of 2 Chronicles 15:13 (le is here a sign of the accusative).

Proclaimed a fast. —An act of national self-humiliation, implying an admission of guilt, and intended to evoke the Divine pity and help. (Joel 2:12–17; 1 Samuel 7:6; Ezra 8:21.)