Verse 17 gives no new information; it says that the command given in verse 15 was carried out.

And God set them in the firmament of the heavens: set means “to place, put.” Them refers to the sun, moon, and stars.

To give light upon the earth is the same as in verse 15.

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .