en_tn_condensed/2ch/25/19.md

your heart has lifted you up

This is an idiom that means he had become proud. Alternate translation: "you have become proud" (See: rc://en/ta/man/translate/figs-idiom)

why should you cause yourself trouble and fall, both you and Judah with you?

Jehoash used this rhetorical question to warn Amaziah not to fight with him. It can be translated as a statement. Alternate translation: "you should not cause yourself trouble and fall, both you and Judah with you." (See: rc://en/ta/man/translate/figs-rquestion)

fall

Here "fall" is a euphemism for "die." (See: rc://en/ta/man/translate/figs-euphemism)