en_tn_lite_do_not_use/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/jit/figs-metonymy)

at the coming of our Lord Jesus

"when Jesus comes back to earth"

with all his holy people

"with all those who belong to him"