And now your two sons, Ephraim and Manasseh, who were born unto you in the land of Egypt before I came unto you into Egypt, are mine; as Reuben and Simeon, they shall be mine.
Read Chapter 48
Ambrose of Milan
Joseph hurried to receive a blessing. Indeed, he presented his sons Manasseh and Ephraim, and Jacob blessed them. Because Jacob had twelve sons, and Paul, as one chosen later, was going to be the thirteenth apostle, a thirteenth tribe would thus be sanctified from the descendants of Manasseh and Ephraim, and divided between them both. Thus Paul would not appear outside the enumeration of the tribes of the fathers; as an outstanding preacher of the Old and the New Testaments, he would readily confirm that the inheritance of a father’s blessing was of help to himself as well.
And we the last became the first through faith, and the nation of the Gentiles inherited the glory of the firstborn. They obtained that honor through obedience and faith. And Christ himself testified about them by saying, “A people whom I did not know served me, with their ear’s hearing they obeyed me.” Even though we were born from a mother of different kinds, since the church was called among different nations, Christ is sufficient for us as a mediator, who unites us to God the Father, and ascribes some to the lot of the saints, and gives them the right glory and declares us to be a holy generation. But see how through Jacob’s love for Joseph he placed the sons of Joseph among his own sons. And so we are also beloved in Christ, and after we were born again through him in a spiritual generation, we are received by the Father, as I have already said, and added to the saints who preceded us. In fact, if we have been called children of God the Father, we also must be under the power and ...
This clearly shows [that Jacob makes Ephraim and Manasseh his own]. Since Jacob had twelve sons, to whom the twelve tribes owed their existence, he distributed the two sons of Joseph into two tribes; and so the tribes became thirteen as the tribe of Joseph was divided between his two sons. And therefore Paul himself, the apostle, was related to these events. After being chosen among the tribes, he was counted the thirteenth after the apostles, and so he was sent to the Gentiles as apostle.