Psalm 127 tells us that children are a gift from the Lord. A child is not our own but on loan from God. God instructed the Hebrews to train up their children and teach them to love God with all their heart, soul, and might (Deuteronomy 6:4-15). Through the Apostle Paul, God commands fathers to bring up their children in the discipline and instruction of the Lord (Ephesians 6:4). Clearly, God expects his people to disciple the kids he blesses us with in the way of the Lord.
In churches that don't baptize infants, a baby dedication serves as a moment in a Christian worship service when the parents stand before the congregation and publically commit to obeying God and raising up their children to know and love God.
Some Christians have read the Bible and conclude that a New Testament baby dedication is done by baptizing the infant. They correctly argue that circumcision was an Old Testament covenant sign that a child was born into God's covenant people. But from that idea, they suggest that baptism replaces circumcision and is a sign of entry into God's family. This logical argument makes sense in light of the Old Testament, but it's not an argument made by the New Testament.
First, John says entry into God's family as a child of God is made possible through faith in Jesus, not the covenant marked by circumcision. Jesus fulfilled that covenant so now all who receive Jesus, who believe in his name, he gives the right to become children of God (John 1:12). But what does it take to be identified as part of the local church? If the Bible commands that we submit to our spiritual leaders and be a part of church discipline, how do we know who is a part of that covenant community? I'll come back to this in a moment.
Next, New Testament baptism is continually referred to as a baptism of repentance, not a baptism of acceptance or a baptism of covenant. Peter discusses the wicked world and the flood in Noah's time. The eight righteous people on earth were brought safely through the water by trusting in the Lord. Jesus suffered once for sin so--like the ark brought people safely through the flood--Jesus can bring us safely to God. Peter says baptism corresponds to this as an appeal to God for a good conscience, through the resurrection of Jesus Christ (1 Peter 3:18-22).
Finally, there was a great debate about circumcision in the First Century. Some argued that Gentiles had to be circumcised before they could enter the local church and call themselves Christians. In fact, this was the topic of the very first Church Council (Acts 15). That council, led by the Apostles, determined that circumcision was not a necessary act of Christianity and therefore not a necessary sign of entry into God's New Testament covenant community. The covenant is through Jesus, not the Law because Jesus fulfilled the Law in the New Covenant. Through the entire discussion about circumcision and the arguments that played out in Paul's letters, there's not a mention of baptism replacing circumcision.
Paul discusses a theology of circumcision in Romans 2:25-29. He says, "For circumcision indeed is of value if you obey the law, but if you break the law, your circumcision becomes uncircumcision" (Romans 2:25). He goes on to argue that the New Covenant is not one of outward signs, but a matter of the heart. It is by the Spirit, not by the letter. In many ways, we might think of circumcision like we think of temples. They were very necessary in the Old Covenant, but in the New Covenant of Jesus Christ, the perfect fulfillment of the Law through Jesus means they are finished. Circumcision was replaced by Jesus, not baptism.
But how do we know who is in the faith community if it's not by circumcision?
The good news is we don't have to do a check to see which dudes are in and which aren't. That was only physical anyway. In Acts, when the Church was instituted, we see people added to their number (Acts 2:37-41). How were they added? Through circumcision? No. Acts 2:41 says, "So those who received his word were baptized and there were added that day about three thousands souls." Peter preached the gospel of Jesus Christ. Those who received Jesus, believed Jesus is who he says he is, and repented (turning from their sinful way to follow Jesus' way). It says they were also baptized, which is the outward sign of the condition of the heart. It's a profession of their belief and the first step in following Jesus.
God's covenant with the Jewish people was (and is) about a physical people through the letter of the Law. God's covenant with his regenerate children is through Jesus Christ who fulfilled the Law. Jesus' Church is not about physical presence or outward signs (which is why there are many who sit in the pews Sunday after Sunday but are still not a part of the Church). It's about belief and repentance. Therefore, the old need not be replaced because it has been fulfilled.
So if the baby dedication is not a "dry baptism" as it has been called from time to time, why do it? If we're not going to baptize babies, what's the point?
The baby dedication is not about bringing unbelieving infants into an organization; it is about that infant's parents proclaiming to the faith-family that they commit to training up the child in the knowledge and love for God so that when the child is able and ready, there is ample opportunity for God to regenerate that child, causing him or her to profess belief, repent, and even be baptized. By standing in front of the congregation, the parents are asking the faith-family to hold them accountable to this monumental task. The baby dedication is not about the baby, it's about the parents.