זוהר בראשית — דף רכו ע”א

Gad is the warrior tribe of Israel, marching at the head of the camp in battle. Rabbi Shimon interprets the verse "Gad, a troop shall attack him" as an allusion to Gad's military role. All the armies that fought before Israel came from Gad. The consolation is that Gad will lead Israel even in the final redemption. Thus Jacob's blessing to Gad points to the tribe's military and messianic role.