Here "Rezin" represents himself and his army. Alternate translation: "Therefore, Yahweh will bring Rezin and his army against the people of Israel" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
The phrase "stir up" is an idiom that means to incite them to attack. Alternate translation: "Yahweh will cause Israel's enemies to attack" (See: [[rc://en/ta/man/translate/figs-idiom]])