What does Genesis 49:23 mean?

The future of the tribes of Israel (Genesis 35:10–11), each descended from a son of Jacob (Genesis 49:1–2), is being foretold. After prophesying over ten of his sons, Jacob comes to the children of his dearest wife, Rachel. This begins with Joseph. This most favored son (Genesis 37:3) was referred to as a fruitful bough by a spring (Genesis 49:22). Now Jacob shifts to emphasize Joseph's ability to defend himself from attack.

These comments express truth on several different levels. Joseph himself was bitterly attacked during his lifetime. He was mocked and eventually sold into slavery by his brothers (Genesis 37:18–36). He was falsely accused of attempted rape by Potiphar's wife and wrongly imprisoned for years (Genesis 39:11–20). He was forgotten and abandoned by Pharaoh's cupbearer (Genesis 40:23). In all these cases, Joseph continued to "fight back" by trusting God to provide for him.

Jacob's oracle also seems to be pointing forward: to the time when two tribes descended from Joseph will be attacked by Israel's enemies. Many of the Old Testament's renowned warriors, such as Gideon, Joshua, and Deborah, will come from the tribes of Manasseh and Ephraim.