This verse repeats statements made elsewhere, using the same language; see 28.1 for the whole verse.

Obey the voice of the LORD, and keep all his commandments: these two clauses mean the same.

I command you this day: Moses is the speaker.

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on Deuteronomy. (UBS Helps for Translators). New York: UBS, 2000. For this and other handbooks for translators see here .