John Calvin Commentary Genesis 48:19

"And his father refused, and said, I know [it], my son, I know [it]. He also shall become a people, and he also shall be great: howbeit his younger brother shall be greater than he, and his seed shall become a multitude of nations." — Genesis 48:19 (ASV)

He also shall become a people. Jacob does not dispute which of the youths will be the more worthy, but only pronounces what God had decreed within himself concerning each, and what would take place after a long time. Therefore, he seeks no causes elsewhere but is content with this one statement: that Ephraim will be more greatly multiplied than Manasseh.

Truly, our dignity is hidden in the counsel of God alone, until, by his vocation, he makes it manifest what he wills to do with us. Meanwhile, sinful emulation is forbidden, as he commands Manasseh to be content with his lot. Therefore, they are altogether insane who hew out dry and perforated cisterns in seeking causes of divine adoption; whereas, Scripture everywhere defines in one word, that those whom God has chosen are called to salvation (Romans 8:29), and that the primary source of election is his free good pleasure.

The form of the benediction, which is related shortly afterward, more fully confirms what I have alluded to: that God's grace toward both is commended, so that Manasseh, considering that more was given to him than he deserved, might not envy his brother. Moreover, this blessing pronounced on Ephraim and Manasseh is not to be taken in the same sense as the former one, in which it is said, In thy seed shall all nations be blessed. Instead, the simple meaning is that God's grace should be so conspicuous toward the two sons of Joseph as to provide the people of Israel with a formula by which to express their good wishes.