John Calvin Commentary Deuteronomy 33:17

"The firstling of his herd, majesty is his; And his horns are the horns of the wild-ox: With them he shall push the peoples all of them, [even] the ends of the earth: And they are the ten thousands of Ephraim, And they are the thousands of Manasseh." — Deuteronomy 33:17 (ASV)

His glory is like the firstling. Translators obscure the meaning by translating the word firstling in the nominative case. However, I have no doubt that he compares the glory of Joseph to the size of a very fine young bull, as if He had said, “His beauty is as of the most choice young bulls in his herds.”

At least it is very consistent that the word firstling should be used for pre-eminent. He says, then, that no more magnificent or glorious young bulls would be found in the land of Joseph than the people itself would be. And to beauty he adds strength and vigor, so that they should be victorious over all their enemies.

At the end of the verse (as I have stated before), he declares that what he had prophesied of Joseph would be common to the two families of Ephraim and Manasseh. At the same time, he confirms the declaration of Jacob, by which he had preferred Ephraim the younger to the elder.

Manasseh, therefore, only reckons his thousands, but Ephraim his ten thousands. God had given proof of this fact in the census already recorded, in which the tribe of Ephraim was found to be more numerous.