Numbers 25:12

Wherefore say, Behold, I give unto him my covenant of peace:

The promise belongs to the time when Israel joined himself unto Baal-peor, when those who followed Baal-peor were destroyed while those who remained faithful to the Lord lived. The Phinehas to whom it was given was the son of Eleazar, the son of Aaron the priest. He acted decisively against open wrongdoing by thrusting through the Israelite man and the Midianitish woman, thus executing judgment against the offenders.

His action came after a plague in which twenty and four thousand died, and after he acted the plague was stayed. Because he was zealous for God, his act turned divine wrath away from the children of Israel so they were not consumed in jealousy, and it made an atonement for the people. For that zeal God gives him His covenant of peace. The covenant of peace included the covenant of an everlasting priesthood to him and to his seed after him, for Phinehas and his descendants.

The covenant of peace marks the distinction between obedience to God and disobedience. It is a covenant of grace in which mercy is extended to those who repent, love God, and desire to serve Him, and He supports them in their trials. God grants the covenant to those who fear and serve Him as a gift of grace through which He becomes their wisdom, sanctification, and righteousness and enables them to honor His character.

These things happened for ensamples and are written for admonition upon whom the ends of the world are come, so that he that thinks he stands should take heed lest he fall, trusting that God will not suffer temptation above what can be borne but will make a way to escape.