en_tn/2ch/20/15.md

all Judah and you inhabitants of Jerusalem

Here "Judah" refers to the people who live there. Alternate translation: "all you who live in Judah and Jerusalem" (See: rc://en/ta/man/jit/figs-metonymy)

for the battle does not belong to you, but to God

This means that God is in control of the battle and of what happens.