en_tn/isa/58/09.md

Yahweh continues speaking to the people of Israel.

then your light will rise in the darkness, and your darkness will be like the noonday

This means their acts of kindness will be examples of light in the community, and the "darkness," the bad deeds, will be overcome by the light. (See: rc://en/ta/man/translate/figs-metaphor)