“Of Benjamin he said,
The beloved of Yahweh shall dwell in safety by (on) him;
He covers him all the day long,
And he dwells between his shoulders (or ‘weapons'). ”
As Benjamin had been the beloved son of Jacob (Genesis 42:4), his tribe were likewise the beloved of Yahweh. He would dwell in safety near God. God would cover him all day long and sit him on His shoulders (compare Deuteronomy 1:31 where Israel are borne like a man bears his son). Like the young Benjamin in Jacob's family he would be a great favourite.
Even indeed when Benjamin sinned deeply God caused them to be preserved in Israel (Judges 19-21) but that was not anticipated here.
So Benjamin is loved by Yahweh and safe under His protection. Dwelling between the shoulders probably means God is, as it were, carrying him on His shoulders. There is no seeming direct connection with Genesis 49:27 where their strength and durability is prominent, except in that those who are covered by Yahweh and carried on His back would certainly be strong and durable.
“Shoulders (katheph).” At Ugarit ktp is probably used signifying weapons. Thus the idea here could be of Yahweh strengthening them in battle, making them mighty men.