What does Genesis 48:12 mean?

Jacob, on his death bed, is preparing to give his formal blessing to Joseph's two sons Ephraim and Manasseh. Jacob has just embraced them and kissed them, pausing to marvel at God's great gift of allowing him to see his son Joseph alive again and even to see Joseph's offspring. It is a tender moment (Genesis 48:1–11).

Now Joseph responds by bowing with his face to the ground before his father in a sign of great respect. The action may also have expressed his own gratitude to God and to his father for the privilege of seeing his own sons blessed by Jacob.

First, though, Joseph is said to have removed his sons "from [Jacob's] knees." This is a somewhat confusing line. It is likely that Joseph's two oldest sons are well into their twenties by this point. Thus, it is unlikely they were sitting on Jacob's lap. What's more likely is that Jacob was seated, and the two boys were close to him as he embraced them. Joseph, preparing for the official blessing, is now moving them into position (Genesis 48:13).