Now we can readily gather from all this that circumcision was very useful and good, as St. Paul declares — not indeed on its own account but on account of the word of God. For we are convinced, and it is the truth, that the children who were circumcised on the eighth day became children of God, as the words state, "I will be their God" [Gen. 17:7], for they received the perfect and full circumcision, the word with the sign, and did not separate the two. God is present, saying to them, "I will be their God"; and this completed the circumcision in them. Similarly, our children receive the complete, true, and full baptism, the word with the sign, and do not separate one from the other; they receive the kernel in the shell. God is present; he baptizes and speaks with them, and thereby saves them.
But now that we have grown old, the pope comes along and the devil with him and teaches us to convert this into an opus legis or opus operatum. He severs word and sign from each other, teaching that we are saved by our own contrition, work, and satisfaction. We share the experience related by St. Peter in II Peter 2:22: "The dog turns back to his own vomit, and the sow is washed only to wallow in the mire." Thus our sacrament has be come a work, and we eat our vomit again. Likewise the Jews, as they grew old, ruined their good circumcision performed on the eighth day, separated the word from the sign, and made a human or even a swinish work out of it. In this way they lost God and his word and now no longer have any understanding of the Scriptures.