Deuteronomy 33:17

17His glory is like the firstling. Translators obscure the meaning by translating the word firstling in the nominative case. I have no doubt, however, but that he compares the glory of Joseph to the size of a very fine bullock, as if He had said, “His beauty is as of the most choice bullocks 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 bullocks should 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 before stated,) he declares that what he had prophesied of Joseph should be common to the two families of Ephraim and Manasseh. At the same time he confirms the declaration of Jacob, whereby he had preferred Ephraim the younger to the elder. Manasseh, therefore, only reckons his thousands, but Ephraim his tell thousands, a proof of which fact God had given in the census which has been already recorded, in which the tribe of Ephraim was found to be the more numerous.