I'm planning, momentarily, to return to a new series on the imputation of Christ's righteousness, but have been too busy recently to post anything. I did contribute this morning to a discussion about baptism and union with Christ on an email list and I'm reproducing the essence of my comments below.
Water baptism formally marks one's inclusion in the body of Christ. This gets at the heart of what it means to hold to infant baptism. The union with Christ (with accompanying privileges and obligations) which is accessed by faith belongs by covenantal promise to baptized infants. For this reason I urge parents to raise their baptized children as Christians and to summon them, even when they are two, to be prophets, priests and kings!!!
Consider the historic Form for the Baptism of Infants used in continental Reformed churches: "When we are baptized into the Name of the Son, God the Son promises us that He washes us in His blood from all our sins and unites us with Him in His death and resurrection. Thus we are freed from our sins and accounted righteous before God. When we are baptized into the Name of the Holy Spirit, God the Holy Spirit assures us by this sacrament that He will dwell in us and make us living members of Christ, imparting to us what we have in Christ, namely, the cleansing from our sins, etc." Then we pray before the baptism that God will graciously look upon the child and incorporate him by His Holy Spirit into His Son Jesus Christ so that he may be buried with him by baptism into death and raised with him to walk in newness of life.
Every time, it seems, anyone talks about union with Christ through baptism, someone else objects, pointing out that union with Christ is enjoyed only through faith (and not baptism). Answer 20 or 32 of the Heidelberg Catechism is usually appealed to in this connection.
No one disputes that we become members of Christ by faith. What is not always acknowledged, however, is that the privileges and obligations of believers belong, by virtue of covenantal promise, to baptized infants.
I've long been fascinated by the uniqueness of the Greek preposition eis (which means "in" or "into") in certain NT formulations. I once heard Sinclair Ferguson say that, so far as he knows, the Pauline expression "believe into (eis) Christ" is completely unique to the Bible and is not found anywhere in extra-biblical koine or classical Greek literature. What I find fascinating is that this is the same preposition used in the expression "baptism into Christ" as in Galatians 3:28 (lit. trans.): "For as many into Christ were baptized (eis Christon ebaptisthete) were clothed in Christ."
So we believe into Christ and we are baptized into Christ. It might seem like two separate unions, but it's not. The union with Christ which is accessed by faith belongs by covenantal promise to baptized infants. The privileges and obligations of membership in Christ are like oversized garments for these infants. But we, their parents, summon them to grow into them. Those who shirk from their membership in Christ in unrepentance will be cut off from Christ (John 15).