Once more, A debt may be charged upon the principal debtor, after a Surety’s satisfying the obligation, in case the Surety’s name was not at first in the same obligation, but is admitted afterward by voluntary contract, covenant, and consent. For, there the covenant is the only determining rule of all matters concerning the discharge. Why are they not sacrificed and glorified immediately after their coming into the world (these being effects of the death of Christ) but because the covenant provides otherwise.
In the name of Jesus Christ (as as surety) had been originally or at first in Adam’s obligation, then more might have been said for an immediate discharge upon his payment of our debt, and suffering death, but this was not the case, for if it had, then his suffering death had been necessary and unavoidable, though no New Testament had ever been made, yea, the making of it had been unnecessary, vain and useless.
Whereas it was extremely necessary, there could have been no transferring of our guilt to him, without it, and his submitting to death was by voluntary contract, Joh. 10: 17,18. And his name not being at first in our bond, hence, his payment was a refusable transaction.
It was by an act of free grace that he was admitted to undertake for us, and his payment accepted in our stead, and so though he paid the idem, the same that we did owe, yet there was nothing contrary to justice or equity, if the Father added terms than before, and so no need that we should be ipso facto discharged. And the law passes sentence not only upon sinful actions, but upon the persons for them, Gen. 2: 17, Gal. 3:22. And, therefore, no justification, till delivered out of this state, which is at union with Jesus Christ and faith.
Samuel Petto, The Difference Between the Old and New Covenant Stated and Explained (London: Printed for Eliz. Calvert, at the Sign of the Black Spred-Eagle at the West end of St. Pauls, 1674), 282- 284. [Some minor reformatting; italics original; some spelling modernized; and underlining mine.]