John Gill Commentary 2 Chronicles 20:4

"And Judah gathered themselves together, to seek [help] of Jehovah: even out of all the cities of Judah they came to seek Jehovah." — 2 Chronicles 20:4 (ASV)

And Judah gathered themselves together to ask help of the Lord ,
&c.] To implore his assistance against their enemies, and his protection of them; and they met not in their several cities, but at Jerusalem, as appears by what follows: even out of all the cities of Judah they came to seek the Lord ;
at the temple, where was the ark, the symbol of his presence.