Moses
Deuteronomy 32:47BSB·traditional attribution

For they are not idle words to you, because they are your life, and by them you will live long in the land that you are crossing the Jordan to possess.”

Matthew Henry Presbyterian @wholebiblehenry

Here is, I. The solemn delivery of this song to the children of Israel, Deu 32:44, Deu 32:45. Moses spoke it to as many as could hear him, while Joshua, in another assembly, at the same time, delivered it to as many as his voice would reach.

Commenting on Deuteronomy 32:44-52

John Gill Reformed Baptist @doctorgill

Get thee up into this mountain Abarim,.... Which was near in sight, and pointed at; it was a range of mountains, of which see Num 21:11, unto Mount Nebo; which was one of the mountains of Abarim, and had its name either from its height, or a city of this name, to which it was near, see Num 32:38; Jerom says (b), in his lays...

Geneva Bible Notes Reformed @genevanotes

For it [is] not a vain thing for you; because it [is] your life: and through this thing ye shall prolong [your] days in the land, whither ye go over Jordan to possess it. (x) For I will perform my promise to you, .