Deuteronomy 33:15

15.And for the chief things of the ancient mountains. In these words he shows that no part of the land would be barren. We know that the tops of mountains are generally and uncultivated, or at any rate bear nothing but trees that have no fruit. But Moses affirms that even there also there shall be the richest produce, for which reason, at least in my opinion, he calls the mountains ancient, and the hills lasting, as if being very highly renowned; for their antiquity is not praised, as if they were created before the rest of the world, but these mountains are honorably distinguished as the first-born, because God’s blessing eminently rests upon them. Thus in the blessing of Jacob it is said, “unto the utmost bound of the everlasting hills,” as much as to say, that no corner of these most celebrated mountains should be devoid of fertility. (Genesis 49:26.)

In the next verse he extends generally to the whole land what he had said of the mountains.

Those are wide of the meaning of Moses, who translate what follows: “On account of the good-will of the dweller in the bush the blessing shall come;” and his rendering is altogether barbarous who gives it, “On account of the piety,” etc. My opinion is that the word רצון, retzon, is in the nominative case; for it is quite in accordance with the context that the “favor of God would come upon the head of Joseph;” for, after Moses had magnified His bounty, he now points out its source or cause, viz., that this extraordinary fertility was the result of God’s gratuitous favor. The words of Jacob, “by the God of thy father,” and “by the Almighty,” exactly correspond with these; where also I have explained why Joseph was called a Nazarene among his brethren. (321)

God is called “the dweller in the bush” by periphrasis, with reference to the vision which was presented to Moses on Mount Sinai; for God then appeared a second time as the Redeemer and Father of His people; after having made His covenant with Abraham and Jacob. And this serves by way of confirmation; as if it were said, that the same God who had formerly blessed Joseph by the mouth of His servant Jacob, now repeated the same prophecy, in order to give fuller assurance of its truth.