A diploma has a seal on it, placed there by the faculty and trustees of the school, authenticating what the diploma says. Paul uses that language in Romans 4:11 as he teaches us something about the sacraments.
The covenant sign is a seal of your faith. God ordained a sign of his covenant with Abraham. The heart of the covenant is fellowship between God and his people. It includes the other things promised to Abram, the land, an heir, becoming the father of a great nation, etc., Genesis 17:6, 8. But the heart of covenant fellowship is “I will be your God and you will be my people.” Genesis 17:7. The sign points to the existence of what it signifies. Golden arches point to a fast food place. The sign itself doesn’t feed you. The Bible doesn’t use the word sacrament (nor does it use the word Trinity), but it refers to the signs and seals God has ordained as signs of the covenant. The don’t replace the Word of God, but God has ordained them for us in addition to the Word. They have been described as the Word in visible form. The sign of circumcision pointed to the reality of covenant fellowship, to the reality of Abram’s trust in God. Recognize that the sacraments function in two directions. We are saying something to God, but, even more importantly, God is saying something to us.
“In the sacrament God first comes to believers to signify and seal his benefits. He assures them with visible pledges that he is their God and the God of their children. He attaches seals to his Word to strengthen their faith in that Word (Gen. 9:11–15; 17:11; Exod. 12:13; Mark 1:4; 16:16; Luke 22:19; Rom. 4:11; and so forth). On the other hand, the sacraments are also an act of confession. In them believers confess their conversion, their faith, their obedience, their communion with Christ and with each other. While God assures them that his is their God, they solemnly testify that they are his children. Every observance of the sacrament is an act of covenant renewal, a vow of faithfulness, an oath that obligates those who take it to engage in the service of Christ (Mark 1:5; 16:16; Acts 2:41; Rom. 6:3ff.; 1 Cor. 10:16ff.).”
Herman Bavinck, Reformed Dogmatics, Vol. 4, pages 476–476
Paul also uses the word “seal.” The covenant sign is the seal of the righteousness of faith. The seal adds authentication. A king would use a signet ring to authenticate a document. The practice continues with many legal documents today. The seal presupposes the reality which it seals. The seal authenticates, it does not add to the content of the document. National Israel prided itself on the covenant sign–but too often ignored what it stood for. If Abraham had received the sign first, perhaps that might have helped earn his righteousness. But Genesis 15 precedes Genesis 17 by at least 14 years. The sign seals, authenticates, the righteousness that Abraham already had by faith when he received the sign of circumcision. The seal of the new covenant functions similarly. The Passover looks forward to the work of Christ that is sealed in the Lord’s Supper. Circumcision is replaced by baptism, Colossians 2:11, 12. The outward sign does not redeem. It is a seal of the righteousness of faith in the Redeemer who does save, Galatians 3:26–29. Yet the sign is important, for it is God-ordained. Don’t elide the word “righteousness” from the text. The reality pictured and sealed in the sacraments is not us and what we do, but God’s righteousness. Focus on the promise!
“We have here a remarkable passage with regard to the general benefits of sacraments. According to the testimony of Paul, they are seals by which the promises of God are in a manner imprinted on our hearts,.. and the certainty of grace confirmed…. And though by themselves they profit nothing, yet God has designed them to be the instruments of his grace; and he effects by the secret grace of his Spirit, that they should not be without benefit in the elect.”
John Calvin, Commentary on Romans, p. 164
Because the covenant sign is the seal of faith, walk in the footsteps of the faith of Abraham. Abraham is the father of both Jewish and Gentile believers. Israel had let the sign degenerate into an indication of national distinctiveness. They forgot that God called them to be circumcised in heart and ears. As they trusted in the sign, rather than in the Savior, they rejected Gentile believers. Because Abraham’s faith preceded the sign, Paul says, he is the father of the Gentiles who believe, but did not receive the Old Testament sign. Abraham’s salvation was without human merit. He trusted God, and it was counted to him as righteousness. All who share in his trust share in the righteousness that was imputed to him. But neither is circumcision a barrier to trust in Christ. Paul guards against the possible inference that the Old Testament sign might be a liability. Jewish believers are God’s people, not because of circumcision, but because they walk in the faith of Abraham.
That is what God calls you to do: walk in the faith of Abraham. As important as Abraham is to Paul’s argument, he is not telling you simply to imitate Abraham. Rather, he is pointing you to the One in whom Abraham trusted. Though he lived long before Jesus came to earth, Abraham’s trust was in the coming Messiah. Thus Abraham is relevant to Paul’s argument that you are saved through faith in Jesus Christ. Walk by faith in the steps of Abraham, the man of faith. Abraham’s faith led him to walk in obedience to the Lord, Genesis 18:17-19. Those who walk in the steps of believing Abraham are redeemed. Their sins are forgiven, not because of their works, but because of the faithfulness of the God who saves those whom he calls to be his people.
Whatever your background, whatever your ancestry, whatever your history, the gospel is the same. You are saved, not by works, not by the sign (either Old or New Testament), but by trust in the Savior in whom Abraham believed.