God has given us several means of grace through which He strengthens the faith of those who trust in Christ alone. These means of grace include the sacraments, and the definition of a sacrament is taken up in question and answer 66 of the Heidelberg Catechism.
The catechism looks to today’s passage in order to define the nature of a sacrament, which is fitting because Romans 4:9–12 deals with one of the sacraments of the old covenant, namely, circumcision. Circumcision was a sign — a visible act that pointed beyond itself to an invisible reality. This invisible reality was the fact that Abraham was cut out from the world and set apart unto God through faith alone (Gen. 15:6; 17). It was a visible reminder of the Lord’s promise to cut out of this fallen world a people for Himself. Circumcision, Romans 4 also reveals, was a seal. In the ancient world, a seal marked off ownership — people knew to whom an object belonged based on the seal affixed to it. Thus, circumcision was the mark of God’s ownership, tangible proof that those who bore the mark actually belonged to the Lord and would inherit all His promises if they had faith in Him.
As with circumcision, the new covenant sacraments are also visible and tangible ways in which we are reminded of God’s promises and marked off as His people. Baptism and the Lord’s Supper have no inherent power to make us the children of God. That is, the performance of these rites themselves does not benefit us if we have no faith. We can access the grace available in them only if we believe the gospel. In fact, if we receive the sacraments without faith, we call down curses upon ourselves (1 Cor. 11:27–30).
John Calvin writes in his famous Institutes that a sacrament “is an external sign, by which the Lord seals on our consciences his promises of good-will toward us, in order to sustain the weakness of our faith, and we in turn testify our piety towards him, both before himself and before angels as well as men” (4.14.1). Using elements that we can taste, see, and touch, the sacraments help us, as embodied creatures, to understand spiritual realities. In turn, when we participate in the sacraments, we testify to our faith in God’s promises before a watching world.
We are creatures with both physical and spiritual components. We understand what happens to us physically when we are washed with water and when we eat, and the sacraments portray spiritual realities to us by way of analogies with our physical experience. The Spirit truly washes us clean of sin, and we truly receive necessary spiritual nourishment from Christ. Baptism and the Lord’s Supper help us understand these truths better.