If Spirit baptism is the most important baptism, why was water baptism continued? Before Pentecost, water baptism was an open statement of repentance and belief in Jesus Christ who was to come (Acts 19:4). After Pentecost, it is still connected with repentance but also a statement of identification into Jesus as Savior and Lord (Acts 2:38, Acts 19:5). But if men can be baptized with the Spirit without water baptism, what is the purpose of water baptism?
From scripture, I think we can say that water baptism today is for the following reasons:
First, it was commanded by Jesus. "And Jesus came and spoke to them, saying, 'All authority has been given to Me in heaven and on earth. Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you; and lo, I am with you always, even to the end of the age.' Amen" (Matthew 28:18-20). The baptism here is obviously water baptism, because men cannot baptize with the Holy Spirit. If we had no other reason to baptize in water, this would be enough. There is no indication in scripture (either by teaching or example) that this direction from the Lord was changed.
Secondly, as we have seen from accounts in the book of Acts, water baptism is God's chosen way for a believer to declare their faith in Christ as Savior. It is an open act, before God and men, of faith in the heart. God could have chosen some other way, such as signing a confession or some other act. But from the teaching and accounts we have, we see that this is God's chosen way for a person to declare their decision to turn their back on the world and follow Jesus.
Thirdly, scripture links water baptism not only to repentance which should proceed baptism, but also to "cleansing from sins" (see Acts 22:16, Titus 3:5). Water baptism by its very nature is a "washing" and scripture indicates that in this act of faith, God performs an inner work of washing the conscience of past sins (1 Peter 3:10). For this to be a true experience, I believe we must emphasize that the person being baptized must be moving in faith before God, with some understanding of what they are doing and what they expect God to do in them and for them as they obey Him. In other words, water baptism is as effective for the believer as the faith they bring to the event. A person coming to be baptized just because it is the "thing to do" is unlikely to experience any significant work of grace in their lives. But a believer that comes expecting God to do something for them will be rewarded by a faithful God who sees the heart being expressed in obedience.
Fourthly, other scriptures link baptism to a burial with Christ (Romans 6:4, Colossians 2:12). The person going under the water is "going into a grave" so to speak, and unless they are raised up, they are dead to this world. The same thing we have said about "washing" can be said about this aspect. If the person being baptized is not moving in faith, it is highly questionable that they will experience anything significant in their baptism. But if by obeying God in the outward act of water baptism they are declaring what is in their heart, namely: "I am turning my back on this world and dying to it with Christ," then God is there to meet them and make that a reality. Faith is the key and experience of God's grace is the result of faith.
Finally, it is very symbolic of what God does in spiritual baptism and should lead to that. It pictures death and resurrection with Christ. It also symbolizes submersion into God in the Spirit. Water is used throughout scripture as a symbol of the Holy Spirit. Submitting to a member of the Body of Christ in baptism symbolizes a release of control and trust in another to raise us from the waters of death.
The act of baptism itself is similar to the bread and cup of the Lord's table. No outward act alone can do what can only be done by God as we respond to His word in faith. We partake of the elements of the Lord's table as an outward expression of what we are doing inwardly before God. Water baptism has the same value. It is an outward expression of faith from an inward reality of dealing with God. It is faith revealed by deeds (James 2:18).
There is a statement by Peter concerning baptism that summarizes what we are saying. "There is also an antitype which now saves us—baptism (not the removal of the filth of the flesh, but the answer of a good conscience toward God), through the resurrection of Jesus Christ, who has gone into heaven and is at the right hand of God, angels and authorities and powers having been made subject to Him" (1 Peter 3:21-22). An "antitype" is the reality which the "type" represents. In this passage, the type referred to is Noah who was "saved through water." So what is the antitype or real baptism that saves us? According to Peter in this scripture, it is the clearing of our conscience before God, of sin, on the basis of the resurrection of Jesus Christ.
I think this takes us back to the baptism of Christ in the Jordan, and to Calvary. Christ's baptism in the Jordan was prophetic, and Calvary combined with Pentecost was the fulfillment. Consider this statement by Paul: "For if when we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life" (Romans 5:10). If we understand salvation to include the whole working of God (namely that we have been saved, we are being saved, and we will be saved), then let us interpret this statement by Peter with that in mind. How is our conscience cleared before God? It is as we know that our past sins are forgiven and that we are living above sin by the power of the Holy Spirit dwelling within.
Our problem in our understanding comes when we try to make salvation a "thing" instead of a person. Scripture reveals that repentance, water baptism, and Spirit baptism work together to bring us into union with Christ Jesus. In this union, everything that God did for us in Christ becomes ours. Each aspect is important, but they are not the same. They are all part of one movement by God to bring us into union with Himself. Jesus is our salvation, not an experience (see 1 Corinthians 1:30). God has made Him to be all things to us.
In summary, I see that water baptism as an act of faith has benefits to both us and God. I see it as a declaration of repentance from sins and faith in Jesus as Savior that is expressed by an act of our will (i.e., faith revealed by works). The effect in a believer moving in faith is a washing away of the past sins, resulting in a clear conscience before God. The old life is buried in a watery grave and a new life with the risen Christ is begun. It is also an open testimony of faith before others that has value in God's eyes (an open confession of Jesus as Lord). With this clear conscience the believer is now ready for the baptism with the Spirit by Jesus which brings us into union with God, where everything Jesus did at Calvary enables us to live the very life of God.