Ephesians 4:4-6 (see also 1st Corinthians 12:13)
There is one body and one Spirit, just as also you were called in one hope of your calling; one Lord, one faith, one baptism, one God and Father of all who is over all and through all and in all.
John Calvin comments: “One baptism. They are mistaken who infer from this that Christian baptism is unrepeatable, for the apostle does not mean this, but that one baptism is common to all, so that, by means of it, we are initiated into one soul and one body. ... We must necessarily acknowledge that the ordinance of baptism proves the three Persons in one essence of God.” (Calvin’s New Testament Commentaries: Galatians, Ephesians, Philippians and Colossians, p.173, emphasis mine)
Whereas Calvin interprets Ephesians 4:5 as the ordinance of water baptism, The Christian Jew Foundation interprets a spiritual baptism: “The ‘one baptism’ referred to here is the baptism of the Holy Spirit which places us in the body of Christ. Please notice carefully the seven things referred to in this passage. God says, ‘There is one body, and one spirit, even as ye are called in one hope of your calling; one Lord, one faith, one baptism, one god and father of all, who is above all, and through all, and in you all.’ The seven things referred to here are all spiritual; so, therefore, the baptism referred to in this passage must also be spiritual. There is not one drop of water in this baptism. This is strictly dry baptism.” (Christian Jew Foundation)
In the debate of immersion vs. sprinkling, both are of the physical realm, whereas the new birth is of the spiritual realm. “That which is born of the flesh is flesh, and that which is born of the is Spirit is spirit.” (John 3:6)
In new birth, the Holy Spirit is the One who makes you born again. (John 3:3) Revelation 7:14 states: “…they have washed their robes and made them white in the blood of the Lamb.” You have a soul and a spirit, neither of which you can see nor touch, from this realm, and yet you have both. In the sanctification of the new birth, the Holy Spirit bathes your soul and spirit in Christ’s blood, with the result that your spirit, and the Holy Spirit, become “one spirit.” (1st Corinthians 6:16-17)
Consider 1st Corinthians 12:13, which states: “For by one Spirit we were all baptized into one body, whether Jews or Greeks, whether slaves or free, and we were all made to drink of one Spirit.” What body is that? It is the Body of Christ. We have a spiritual baptism into the Body of Christ when what?
Adrian Rogers comments: “We are baptized by the Holy Spirit into the Body of Christ. When does this take place? When we believe in the Lord Jesus Christ, when we receive Christ as personal Savior, two things take place at the same time: We are baptized into the Body of Christ, and we are filled with the Spirit. We’ve all been baptized into His body and have all been made to drink into one Spirit. That is, the Holy Spirit of God, when I give my heart to Jesus, and I say, ‘Lord Jesus, I’m a sinner. I can’t save myself. You died to save Me. You promised to save me if I would trust You. I do trust You. Once and for all, now and forever, forgive my sin, come into my heart, be my Lord and Savior,’ and then a miracle takes place, and the Holy Spirit says, ‘Now I’m placing you, Adrian, into the Body of Christ. I am baptizing you into the Body of Christ.’ Water baptism only symbolizes this Spirit baptism. I am baptized, verse 13, into the Body of Christ. But not only am I placed into the Body of Christ, the Holy Spirit is placed into me, and I’ve been made to drink into one Spirit. Just as I take a drink of water, the Holy Spirit just comes in to me. So I am in the Body of Christ, and the Holy Spirit is in me. That takes place when I get saved, and that makes the wonderful transformation, that makes the difference. And so when I am put into the Body of Christ, there I receive my spiritual gift.” (You Are Somebody in His Body: 1st Corinthians 12:12-18; emphasis mine)
Adrian Rogers adds: “Now, who is the Baptizer? The Holy Spirit. Who is being baptized? The believer in Jesus. Into what is he baptized? Into the Body of Christ. When is he baptized? At the moment of his conversion, the moment he gives his or her heart to Jesus Christ and no one is left out. We are baptized by the Holy Spirit into the Body of Christ.” (You Are Somebody in His Body: 1st Corinthians 12:12-18; emphasis mine)
In this spiritual baptism, through which the Holy Spirit indwells the body of the believer (1st Corinthians 3:16), the believer is simultaneously placed in the Body of Christ.