en_tn/1th/03/13.md

strengthen your hearts, so that they will be

Here "heart" is a metonym for one's beliefs and convictions. Alternate translation: "strenghten you, so that you will be" (See: rc://en/ta/man/translate/figs-metonymy)

at the coming of our Lord Jesus

"when Jesus comes back to earth"

with all his saints

"with all those who belong to him"