John Calvin Commentary Genesis 49:19

"Gad, a troop shall press upon him; But he shall press upon their heel." — Genesis 49:19 (ASV)

Gad, a troop. Jacob also makes allusion to the name of Gad. He had been so called, because Jacob had obtained a numerous offspring by his mother Leah. His father now admonishes him, that though his name implied a multitude, he should still have to deal with a great number of enemies, by whom, for a time, he would be oppressed: and he predicts this event, not that his posterity might confide in their own strength, and become proud; but that they might prepare themselves to endure the suffering by which the Lord intended, and now decreed to humble them.

Yet, as he here exhorts them to patient endurance, so he then raises and animates them by the added consolation, that, eventually, they should emerge from oppression, and should triumph over those enemies by whom they had been vanquished and routed; but this only at the last. Moreover, this prophecy may be applied to the whole Church, which is assailed not for one day only, but is perpetually crushed by fresh attacks, until eventually God shall exalt it to honor.