“It is to be remembered that there were two covenants made with Abraham. By the one, his natural descendants through Isaac were constituted a commonwealth, an external, visible community. By the other, his spiritual descendants were constituted a church. The parties to the former covenant were God and the nation; to the other, God and His true people. The promises of the national covenant were national blessings; the promises of the spiritual covenant (i.e., the covenant of grace), were spiritual blessings, reconciliation, holiness, and eternal life. The conditions of the [national] covenant were circumcision and obedience to the law […]. There cannot be a greater mistake than to confound the national covenant with the covenant of grace, and the commonwealth founded on the one with the church founded on the other.”
-Charles Hodge, Church Polity (New York: Scribner, 1878), 66-67
The Sovereign Logos 