Paul tells us in Romans 4:11 that circumcision, and therefore baptism (Col. 2:8–15), is a sign. Now signs, it is well known, point beyond themselves to signify something else, but they are not in themselves that which they signify. For example, a sign on a highway reading “Washington D.C., 23 miles” points to a city 23 miles away, but the sign is not the city of Washington. Likewise, baptism signifies something beyond itself but in itself is not the thing that is signified.
Today’s passage alludes to some of the realities to which baptism points. First is our ingrafting into Christ and His body. In John 15:1–17, Jesus describes Himself as the vine in whom we the branches must abide. We must be ingrafted into this vine by faith — we must enter into a living, vital, and salvific relationship with Him. This idea is prevalent in the New Testament where to believe in the Lord is to believe “into” (from the Greek word eis) Christ. Moreover, when we trust in Jesus we are not alone. The Christian community enters into union with the Savior by believing in His name. If I am in Christ and my friend is in Christ, we experience union with each other in some sense. We all become part of the “one body,” as today’s passage indicates. Paul also describes this union with other Christians in Romans 11:11–24, where believing Gentiles become one with faithful Israelites.
Baptism also signifies regeneration and the remission of sins (John 3:5; Acts 2:38). Apart from the direct work of the Holy Spirit, we are dead in sin and cannot trust in Jesus. He alone can renew our hearts and create a disposition inclined toward God and His Messiah (Eph. 2:1–10). The sacrament of baptism signifies that the Lord has done this for His people — He has regenerated our hearts. Water symbolizes the new life the Spirit brings, and its washing effect points to the cleansing from sin that results from faith in Christ.
Finally, having the sign does not necessarily mean we have the reality. We can trust in the rite of baptism without having faith, and if so, neither ingrafting, regeneration, nor remission has happened. But for those of faith, the Holy Spirit works through baptism to remind them of His work and, consequently, to strengthen faith.
Whenever we read the Nicene Creed we confess belief in the communion of saints. This means that we become united to every believer who has ever lived whenever we trust in Jesus. The other Christians we know are not merely acquaintances; we are one body with them in Christ. Think of some people in your church whom you do not know well. Make plans to get together with them and fellowship as a way to display the unity we all have in Christ.