It will be a covenant of permanent priesthood for him and his descendants, because he was zealous for his God and made atonement for the Israelites.”
That covenant will mean a permanent priesthood for Phinehas and his descendants, because he made atonement for Israel in zeal for his God.
It deepens the reward by tying it to priesthood and atonement.
6Just then an Israelite man brought to his family a Midianite woman in the sight of Moses and the whole congregation of Israel while they were weeping at the entrance to the Tent of Meeting. 7On seeing this, Phinehas son of Eleazar, the son of Aaron the priest, got up from the assembly, took a spear in his hand, 8followed the Israelite into the tent, and drove the spear through both of them— through the Israelite and on through the belly of the woman. 9So the plague against the Israelites was halted, but those who died in the plague numbered 24,000. 10Then the LORD said to Moses, 11“Phinehas son of Eleazar, the son of Aaron the priest, has turned My wrath away from the Israelites; for he was zealous for My sake among them, so that I did not consume the Israelites in My zeal. 12Declare, therefore, that I am granting him My covenant of peace. 13It will be a covenant of permanent priesthood for him and his descendants, because he was zealous for his God and made atonement for the Israelites.” 14The name of the Israelite who was slain with the Midianite woman was Zimri son of Salu, the leader of a Simeonite family. 15And the name of the slain Midianite woman was Cozbi, the daughter of Zur, a tribal chief of a Midianite family. 16And the LORD said to Moses, 17“Attack the Midianites and strike them dead. 18For they assailed you deceitfully when they seduced you in the matter of Peor and their sister Cozbi, the daughter of the Midianite leader, the woman who was killed on the day the plague came because of Peor.”