NOTE: I have modified some of the language in the answer to this question in alignment with my own Baptist convictions.
Question 44: What is baptism?
Answer: Baptism is immersion in water in the name of the Father, the Son, and the Holy Spirit; it signifies our death and resurrection with Christ, our cleansing from sin, and our commitment to belong to the Lord and to his church.
Who should be baptized? Many Christian denominations baptize both those who profess faith in the gospel and the infant children of believers. The reasons for baptizing infants vary from denomination to denomination, but there are basically two reasons some Christians practice it:
(1) Some argue that the act of baptism has some saving effect on the infant, either by cleansing from the stain of original sin (Roman Catholics) or by causing the new birth (Lutherans). These traditions view baptism as a means by which God brings salvation (or at least the beginning of the process of salvation) to the infant.
(2) Others argue that baptism itself does not bring salvation to the infant, but it is God's appointed covenant sign (corresponding to circumcision under the old covenant) to mark out children of believers as covenant members. Not all new covenant members will be saved in the end, according to this view, but we are commanded to apply the covenant sign nonetheless, just as Abraham was commanded to circumcise all his male children.
In contrast to these views, Baptists have long argued that baptism is, by definition, an act of public confession of faith. Since infants cannot confess faith publicly, infants should not be baptized. We should only baptize those who understand that by being baptized, they are publicly identifying themselves as those who trust in Christ alone.
The New Testament consistently links baptism to repentance and faith. John the Baptist specifically denied that baptism was to be given on the basis of one's lineage but was instead only for those who repented of their sins (Matt. 3:1-12). Peter called upon his hearers on the day of Pentecost to "repent and be baptized" (Acts 2:38). When asked by the Philippian jailer what he must do to be saved, Paul responded, "believe in the Lord Jesus, and you will be saved, you and your household" (Acts 16:31). And lest we assume that Paul meant by "household" that infants should be automatically baptized when their parents believe, the very next verse tells us, "And they spoke the word of the Lord to him and to all who were in his house. And he took them the same hour of the night and washed their wounds; and he was baptized at once, he and all his family" (Acts 16:32-33). The text clearly indicates all who were baptized had previously heard the gospel proclaimed to them and had believed it.
The connection between faith and baptism goes back to Jesus' Great Commission, given to his disciples after his resurrection:
All authority in heaven and on earth has been given to me. Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age. (Matt. 28:18-20)
Notice from Jesus' command that the process of making disciples includes initiation by baptism into the triune name, followed by teaching obedience to all that Jesus commands. Baptism stands at the beginning of the process of making disciples, showing that baptism is only for those who are committed to being disciples of Christ. We should apply baptism only to those who are capable of professing faith, because baptism, by its nature, is a confession of faith. It cannot be received properly by one who does not intend to be identified with Christ.
Suggested passage for personal or family reading: Acts 2. How does Peter's sermon lead up to a call to baptism? What is the connection between repentance, faith, and baptism in Scripture? What does this mean for you?