If a police officer issues a summons, you need to pay attention and show up in court. How much more do you need to respond when the summons comes from God, Acts 2:38–39!
Listen to God’s summons. Repent! God’s call (verse 39) might be translated “summons,” see Acts 4:18. It is a call, not only to Israel, but to the nations to repent as the blessing of the Holy Spirit extends beyond the Old Testament covenant people. The command grows out of a conviction of sin, verse 37. Don’t allow the call to repentance to be minimized as you present the gospel. Though it may not be popular to call people to repentance, ambiguity regarding man’s sinfulness makes it impossible to appreciate the depths of God’s grace in Christ. Repentance involves a change of mind, leading to a new life. It not only marks conversion, but also characterizes the entire Christian life this side of heaven. The kingdom belongs to those who have turned (and continue to turn) from sin to Christ. Peter’s command in his Pentecost sermon echoes through the years to your ears as well.
Be baptized! Repeatedly in Acts conversion is indicated by baptism. Note the difference in emphasis from the decisionism and individualism of much contemporary evangelism. (Yes, it is crucial that you personally trust in Christ. Remember that when too many people place their trust, not in Christ, but in the act of baptism. But remember that coming to Christ also implies an involvement with his church.) Baptism is a sign of separation from sin and cleansing from its guilt. Water is the substance that is used in baptism. It seals your union with Christ, Romans 6. It marks you as belonging to your Lord. Christ included the command to baptize in the Great Commission. While baptism does not save, it is important, not just an option. The new covenant (characterized by the Holy Spirit, 2 Corinthians 3:6; Hebrews 10:15,16) has a new sign, non-bloody, administered to females as well as males, and now to believing Gentiles as well. “[B]aptism signifies union with Christ in the virtue of his death and the power of his resurrection, purification from the defilement of sin by the renewing grace of the Holy Spirit, and purification from the guilt of sin by the sprinkling of the blood of Christ. The emphasis must be placed, however, upon union with Christ.” (John Murray, Christian Baptism, p. 8) Peter gives a reason for the command to be baptized.
Respond, because God’s promise is yours. God’s promise still stands. The phrase “the promise” was a familiar one to the Israelites gathered for the feast, one that needed no elaborate identification. What promise would come to the mind of a godly Israelite? The basic covenant promise, “to be your God and the God of your descendants after you,” Genesis 17:7. There had been preliminary fulfillment of that promise: God had walked with Abraham, he had protected his descendants in Egypt and then delivered them and brought them into the promised Land, he had raised up David as the great king, he had brought them back from exile, where they had been sent because of their sins. But that promise had just come to its richest fulfillment as the Messiah having entered the world, had suffered, died, and been raised on behalf of his people. Now the exalted Lord was pouring out his Spirit upon the church, the Spirit who would make God’s holy temple, not a stone structure in Jerusalem, but the hearts of his people. “God has given not only the covenant but also the accompanying signs, circumcision and baptism. He reveals Himself through Christ, but also in Word and sacrament, invisible and visible revelation. Circumcision and baptism are not a stage created by God only for man to profess his fidelity. The sacraments are the opposite—they are the revelatory stage (when accompanied by the Word) by which God heralds His covenant promises and trumpets the gospel of His Son…. To what promise does Peter refer? The promise is undoubtedly weighted n the whole of redemptive history: the protevangelium (Gen. 3:15); God’s promise to Abraham (Gen. 12:1–3; 15; 17:1–14); and his promise to David (1  Sam. 7:14). However, Peter also mentions the gift of the Holy Spirit, which invokes the fulfillment of Joel’s prophecy (2:28–29) and is certainly connected to the promise of the new covenant, which included the promise to children (Jer. 31:31; 32:39; Isa 32:15; 44:3; Ezek. 11:19; 36:26–27; 37:14).” (J. V. Fesko, Word, Water, and Spirit: A Reformed Perspective on Baptism, p. 357)
The promise is for you, your children, and those who are far off. The promise is for you. It is for those who that day, today, and every day until Christ returns, who repent from sin and trust in Christ. It is not a superstitious custom, but a sign and authenticating seal of union with your Savior. Remember your baptism when you begin to doubt. Remember your baptism when you are tempted to sin. The Westminster Larger Catechism uses language that may sound old, but the idea is important. Q. 167. How is baptism to be improved by us? A. The needful but much neglected duty of improving our baptism, is to be performed by us all our life long, especially in the time of temptation, and when we are present at the administration of it to others; by serious and thankful consideration of the nature of it, and of the ends for which Christ instituted it, the privileges and benefits conferred and sealed thereby, and our solemn vow made therein; by being humbled for our sinful defilement, our falling short of, and walking contrary to, the grace of baptism, and our engagements; by growing up to assurance of pardon of sin, and of all other blessings sealed to us in that sacrament; by drawing strength from the death and resurrection of Christ, into whom we are baptized, for the mortifying of sin, and quickening of grace; and by endeavoring to live by faith, to have our conversation in holiness and righteousness, as those that have therein given up their names to Christ; and to walk in brotherly love, as being baptized by the same Spirit into one body.
The promise is for your children. As they were included in the covenant promise to Abraham, they are included here. Not only is there no specific exclusion of children from the covenant, but they are here named as the recipients of God’s promise. This refers, not to all children, but to the children of believing parents. Rejoice in your privileges, covenant children, and respond in faith-full obedience. “The gospel dispensation is the unfolding of the covenant made with Abraham, the extension and enlargement of blessing conveyed by this covenant to the people of the Old Testament period Abraham is the father of all the faithful. Those who are of faith are blessed with faithful Abraham…. If children born of the faithful were given the sign and seal of the covenant and therefore of the richest blessing which the covenant disclosed, if the New Testament economy is the elaboration and extension of this covenant of which circumcision was the sign, are we to believe that infants in this age are excluded from that which was provided by the Abrahamic covenant?” (John Murray, Christian Baptism, pages 51–52)
The promise is for all who are far off. Suddenly the door is thrown open. The Gentiles, those summoned by God, are recipients of the promise. Pentecost marks the focus of the ripple of the gospel spreading throughout the world. The promised blessing of the nations is becoming a reality, Joel 2:32; Isaiah 57:19.
Just as much as Peter’s original hearers on the day of Pentecost, you have been summoned by God to repent and turn to Christ, to be baptized, to live as his covenant people. God calls you to respond to that summons!