en_tn/isa/59/17.md

He put on righteousness as a breastplate and a helmet of salvation upon his head. He clothed himself with garments of vengeance and wore zeal as a mantle

This shows God preparing to punish the wicked people. (See: rc://en/ta/man/translate/figs-metaphor)

mantle

a loose, flowing robe

He repaid them

Isaiah is describing a future event as if it happened in the past. This means that it will certainly happen.