Albert Barnes Commentary Deuteronomy 33:7

"And this is [the blessing] of Judah: and he said, Hear, Jehovah, the voice of Judah, And bring him in unto his people. With his hands he contended for himself; And thou shalt be a help against his adversaries." — Deuteronomy 33:7 (ASV)

Bring him to his people - Moses, taking up the promise of Jacob, prays that Judah, marching forth at the head of the tribes, might always be brought back in safety and victory; arm indicates that God would grant help to accomplish this.