“Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.” (Acts 2:38)
These men here on the day of Pentecost were already “devout men” (pious, godly men; Acts 2:5) and were pricked in the heart and convicted over their sin to such a degree they asked what they needed to do (Acts 2:37). Only a child of God is pricked in the heart by the preaching of the gospel; the preaching of the cross is utter foolishness to the unregenerate (1 Cor 1:21). Peter calls upon those already born again children of God to repent and be baptized.
Remission of our sins before God is not by your belief, repentance, and baptism but only by the blood of Jesus Christ (Heb 9:12, 10:18-20). However, not every child of God sees their sins as remitted apart from that gospel message that tells you that Jesus did pay for your sins on the cross. They don’t “feel forgiven”; they don’t “feel their sins remitted” in their heart when they are pricked in the heart and feel the burden and conviction of their sin. So for those who are pricked in the heart by the gospel, for those that feel a heart burden over their sins, they need to repent, believe, and be baptized by placing their faith in Jesus Christ as their only means of salvation from their sins. When we exhibit faith in Jesus Christ and believe the gospel, we now “feel our sins remitted” in our heart. We go from “feeling condemned” to “feeling forgiven” in our heart as we now have peace in our heart with God through justification by faith (Rom 5:1). In that experiential (not eternal way) those who believe, repent, and are baptized now experience a remission of sins as baptism “doth now save us [not eternal salvation, but now temporal salvation], not the putting away of the filth of the flesh but the answer of a good conscience toward God” (1 Pet 3:21). Their conscience previously pricked and convicted them in a way that they didn’t feel like their sins were forgiven and remitted (even though they were already forgiven by Christ’s blood for these born again men), but now they have the “answer of a good conscience before God” since they have placed their faith in Christ as the only means of their salvation.
When one believes in the Lord, repents, and submits to baptism, they will receive “the gift of the Holy Ghost”. This promise of receiving the gift of the Holy Ghost is not just to these men on the day of Pentecost but also “to your children, and to all that are afar off, even as many as the Lord our God shall call” (Acts 2:39). So all those that have already been called by God in the new birth, can enact this promise and receive the gift of the Holy Ghost. Now, this is not the new birth. This is not receiving new life in Christ from dead in trespasses and in sins. A dead person cannot “receive” anything; only alive people can receive a gift. Spiritual life is given by the Holy Ghost in the new birth. Now that you have spiritual life and been called by the Spirit (remember only those that the Lord has already called [already been born again] are the only people who can receive this gift of the Holy Ghost), if you believe on Christ, then you will receive this gift and feel a special assurance of the Holy Ghost witnessing that you are indeed a child of God. “In whom [in Christ, v12] ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise” (Eph 1:13) After you believe the gospel, you are not born again (these men in Acts 2 were already born again men pricked in the heart, unregenerate men are only cut to the heart, Acts 5:33, 7:54), but after belief you are now “sealed with that Holy Spirit of promise” giving you assurance of salvation. This is when “the Spirit itself beareth witness with our spirit, that we are the children of God” (Rom 8:16). All of God’s born again (already called in the new birth) children receive a witness of sonship and assurance of salvation in their heart when we believe in Christ, repent of our sins, and follow Christ’s example in baptism. When you believe and are baptized is not when the filth of your flesh is put away and your sins are forgiven (that was accomplished by the blood of Christ on the cross), but that’s when those who are pricked in the heart with conviction over their sins, feel peace in their heart and the answer of a good conscience before God.