en_tn/gen/01/15.md

Let them be lights in the sky to give light upon the earth

This is a command. By commanding that they should light the earth, God made them light the earth. (See: rc://en/ta/man/translate/figs-imperative)

to give light upon the earth

"to shine light on the earth" or "to brighten the earth." The earth does not self-shine but it is lit and so reflects light.

It was so

"It happened like that" or "That is what happened." What God commanded happened just as he said it should. This phrase appears throughout the chapter and has the same meaning. See how you translated this in Genesis 1:7.