Moses
Deuteronomy 29:12ESV·traditional attribution

so that you may enter into the sworn covenant of the LORD your God, which the LORD your God is making with you today,

Matthew Henry Presbyterian @wholebiblehenry

It appears by the length of the sentences here, and by the copiousness and pungency of the expressions, that Moses, now that he was drawing near to the close of his discourse, was very warm and zealous, and very desirous to impress what he said upon the minds of this unthinking people.

Commenting on Deuteronomy 29:10-29

John Gill Reformed Baptist @doctorgill

That thou shouldest enter into covenant with the Lord thy God,.... That is, they were all to appear and stand in this order before the Lord, that they might solemnly avouch him to be their God, and hear him declaring them to be his people, and the many promises and prophecies of good things he should deliver to them, as well as threatenings of wrath...

Geneva Bible Notes Reformed @genevanotes

That thou shouldest enter into covenant with the LORD thy God, and into his oath, which the LORD thy God maketh with thee this day: (g) Alluding to them, that when they made a sure covenant, divided a beast in two, and past between the parts divided, .