en_tn/2th/01/10.md

when he comes on that day

Here "that day" is the day when Jesus will return to the world.

to be glorified in his holy people and to be marveled at by all those who believed

This can be stated in active form. Alternate translation: "so that his holy people will glorify him and all those who believed will marvel at him" or "so that his people will glorify him and all those who believed will stand in awe of him" (See: rc://en/ta/man/translate/figs-activepassive)