If salvation is the baptism in the Holy Spirit by Christ, graciously given to those who repent and believe, calling on the name of the Lord, and if it does not need water baptism to be effected, then what might water baptism be?
1] One can do it in raw obedience without a theology. "Jesus said to do it so I'm doing it."
2] It can be like John's baptism, a statement of repentance.
3] It can be a repentant someone who has come to belief and is calling on God as St. Peter said "Baptism, which corresponds to this, now saves you, not as a removal of dirt from the body but as an appeal to God for a clear conscience, through the resurrection of Jesus Christ..." (I Peter 3:21)
4] It can be symbol of our baptism in the Holy Spirit and our participation in the death and resurrection of Christ. See Acts 10 and Colossians 2:12
Hebrews 6:2 suggests that the deeper instruction for Christians includes that on baptisms plural. The variety of causes and symbols water baptism enjoys provides that possibility of plural water baptism. Why then do the Scriptures say "One Lord, one faith, one baptism" ?
When the Scriptures speak of "one baptism" it must be that baptism which all the regenerate have necessarily encountered, that of the Holy Spirit. I Corinthians 12:13 "For by one Spirit we were all baptized into one body -- Jews or Greeks, slaves or free -- and all were made to drink of one Spirit."
Simon Magus believed and was baptized in the name of the Lord Jesus and yet St Peter told him, " You have neither part nor lot in this matter, for your heart is not right before God. Repent therefore of this wickedness of yours, and pray to the Lord that, if possible, the intent of your heart may be forgiven you. For I see that you are in the gall of bitterness and in the bond of iniquity." Acts 8:21-23
The core of the Gospel, as far as what God has asked of us in it, is to repent, believe, and call on God. Water baptism can coexist (and does in the Scripture) but only as a reference to either repentance, preparing the way for the Holy Spirit baptism (John the Baptist's) or the convicted person calling on and appealing to God for forgiveness (in other words, acting as and outwardly decorating your prayer for salvation) or as a symbolic statement of what you know has already happened (died and raised with Christ /baptized in the Holy Spirit). In each case it is not necessary to the thing it references. A man can repent, call on God, be baptized in the Holy Spirit without this referrer of water baptism. But Biblically we also can and obediently will use it to so refer. Without the baptism of the Holy Spirit you have "neither part nor lot" in the Kingdom of God and Christ. Baptism can symbolize what we believe but can't reference that alone. It doesn't effect, it represents and it must represent that which has happened or is happening.
Those that can't or won't or haven't repented and called on God should not be baptized. Even if they say that they have, and it is clearly not evident that they have been baptized of the Holy Spirit, baptizing such devalues it. Passed from death to life did you? Big whoop. It is like making baptism a currency (which represents value) and deciding that, while the gold standard is desirable it is too rare, so your parishioner "dollars" will now be backed by mud. You can get it everywhere and even make it yourself!
These "cant',won't, haven'ts" includes 14 year old Southern Baptists who know it is time to walk the aisle cuz mammy knows that Elvis did or the baby of parents trapped by the fears attendant to original sin or unconditional election and want some peace of mind, or your boyfriend who is willing to do what it takes to make you believe that this love will last.
Because of promiscuous baptism, these, and these are without number clogging our assemblies, will misunderstand (how could they not?) and think, with the rest of a superstitious world, that the magic has been done and they will never pass from death to life.