Note the similarities and differences between the blessing of Ephraim and Manasseh, and the blessing of Jacob and Esau. Isaac is nearly blind when he confers the blessing. So is Jacob. The blessing of the older belongs to the younger of the sons in each case. There is some maneuvering with the blessing of both, in the case of Joseph, he positions Ephraim, the eldest, that he might be nearest Jacob’s right hand. In each case, the expected order is switched.
The difference here is that the decision to bless the younger first is deliberate, once again emphasizing that blessing comes not from birth, birth order, or ability, but solely by grace. The lesson is pointedly made in the next chapter as Reuben loses the birthright of the eldest son because of his behavior and that birthright does not pass down the line as we might expect, falling on Judah, but goes to the very end of the line, falling on Joseph (you will see this plainly in 1 Chronicles 5:1).
Jacob is now in Egypt, but he believes his descendants will not stay. They have land in Canaan, and he knows God’s hand will take the family back there as surely as it brought them to Egypt. And so, Jacob, in essence, adopts Manasseh and Ephraim and in this scene, assures Joseph that the boys will receive their rightful place as his sons. When the writer of Hebrews in the New Testament talks about Jacob’s great faith, this is the illustration he uses.
All God’s gifts are by grace, given as he sees fit. People of faith realize that and accept them humbly and gratefully, seeing in them also an assurance of a blessed future.