Christ is called the covenant of God. "I will give thee for a covenant of the people." As Calvin well expounds it, _sponsor foederis_, the surety or undertaker of the covenant, of that second new covenant, between God and His people, not the Jews only, but the Gentiles also. A surety on both sides: the surety of God's covenant to them; "For all the promises of God are in Him, yea, and in Him, Amen." He sees them all made good to the heirs of promise. And Christ again is the surety of their covenant unto God; for He undertakes to make good all their covenants, and vows, and promises unto God. "Those that Thou gavest Me, I have kept," saith Christ. "And I live (saith Paul), yet not I, but Christ liveth in me." So that it is Christ who makes the covenant good on both sides, as God's to His people, so His people's to God; and so it follows in that place of Isaiah, "I have given thee for a covenant to the people, to establish the earth;" establishment must come from Christ, the undertaker, the surety of the covenant; as He paid the debt for the time past, so He must see the articles of the covenant kept for the time to come. For want of such an undertaker or surety, the first covenant miscarried: It was between God and the creature, without a mediator; and so the creature changing, the covenant was dissolved; but the second, God meant should not miscarry, and therefore puts it into sure hands; "I have laid help upon One that is mighty," speaking of Christ, and "I will give Thee for a covenant to the people." God hath furnished Christ wherewithal to be a surety; to make good His covenant to His people, and their covenant to Him.