The Doctrine of Justification by Faith

4. When he would have us in this matter not only come unto the full Assurance of Faith concerning his Promises, but also to have strong consolation therein, he resolves it wholly into the Immutability of his counsel, as declared by his Promise and Oath. chap. 6.18, 19. So that neither is God capable of having any surety properly so called, neither do we stand in need of any on his part for the confirmation of our Faith in the highest degree.

5. We on all accounts stand in need of a surety for us, or on our behalf. Neither without the Interposition of such a surety, could any Covenant between God and us be firm and stable, or an everlasting Covenant, ordered in all things and sure. In the first Covenant made with Adam there was no surety, but God and men were the immediate Covenanters. And although we were then in a state and condition able to perform and answer all the Terms of the Covenant, yet was it broken and disannulled. If this came to pass by the failure of the Promise of God, it was necessary that on the making of a new Covenant he should have a surety to undertake for him, that the Covenant might be stable and everlasting. But this is false and blasphemous to imagine. It was man alone who failed and broke that Covenant. Wherefore it was necessary that upon the making of the New Covenant, and that with a design and purpose that it should never be disannulled as the former was, that we should have a surety and undertaker for us. For if that first Covenant was not firm and stable because there was no surety to undertake for us, notwithstanding all that Ability which we had to answer the terms of it; how much less can any other be so, now our Natures are become depraved and sinful? Wherefore we alone were capable of a surety properly so called, for us, we alone stood in need of him, and without him the Covenant could not be firm, and inviolate on our parts. The surety therefore of this Covenant is so with God for us.