The apostles and prophets gave us teaching by example on the topic of the timing of baptism. We find in the book of the Acts of the Apostles that believing the gospel and getting baptized are closely associated.

Acts 2:38– And Peter said to them, “Repent and be baptized each one of you in the name of Jesus Christ for the forgiveness of sins.
Acts 2:41- The ones therefore who accepted his message were baptized, and about three thousand souls were added during that day.

Other passages in Acts showing immediate baptism are 8:12; 8:36-38; 9:18; 10:47-48; 16:14-15; 16:32-33; 18:8. You were expected to be baptized at the same time as you believed, they are a simultaneous event.

Take for example the Philippian jailer, when he believed, he was baptized “on the spot…in the middle of the night.” (Acts 16:31-34).

In Acts 8:13 Simon the magician was baptized by the apostles even though they knew his heart was not right. But he had professed belief, so he had to be baptized immediately, that is true doctrine and practice.

This doctrine of immediate baptism is so important, that God performed a miracle for the Ethiopian eunuch. In Acts 8:26, the scripture tells us that the road he was on was desert. Yet as soon as the eunuch believed, they saw a body of water deep enough for both Philip and the eunuch to get down into it and the eunuch be baptized. (Acts 8:36)

Have you believed, but are not yet baptized? If so, you are in disobedience to the apostles of Christ, and your leaders are in disobedience, who have neglected to baptize you immediately upon your profession. Satan, the enemy of your soul, wants you to have a cooling down period.

Am I saying that, if say, a man leads 3 people to belief in the gospel on Thursday, that he should not wait until the next Sunday to baptize them? Exactly! I am saying that if he led someone to the Lord during lunch break at work on Thursday, the convert should tell his boss he is leaving his job temporarily in order to find water to be baptized that Thursday afternoon, baptized by the believer who told him the gospel. What a powerful testimony that is, that you drop everything else going on in order to find water and be baptized. You are now dead to the world, so what else matters? Find water, and show everyone that you died and were buried with Christ, and have come out in newness of life, and nothing else matters. Do not allow anything or any human to let you cool down from your first love.

This truth about the timing of baptism has bearing on a couple textual variants in the Greek New Testament text. The biggest one is in Acts 8:37, where it was added to the narrative of the Ethiopian eunuch, where the eunuch had asked, “Look, water. Is there anything forbidding me to be baptized?” Then an addition was made later to the text which says, 37″And Philip said, ‘If you believe with all your heart, it is permissible.’ And he answered and said, ‘I believe that Jesus Christ is the Son of God.’ “

Similar is an addition made to Acts 2:41. Papyrus 74, Codex Sinaiticus, Codices A, B and C, Sahidic Coptic, the Ethiopic, Clement, and Eusebius read: “The ones therefore who accepted his message were baptized, and about three thousand souls were added during that day.”

But later manuscripts read: “The ones therefore who READILY accepted his message were baptized…”But this “readiness” was not for the baptizers to judge. If the person accepted the message and professed belief, they were to be baptized, period.

The bishops had later decided that there should be some kind of “probationary period” to see whether the convert was serious or not. They also made baptism something only “clergy” could perform, but this is not indicated by the example and teaching of the apostles.

At the same time, since believing the gospel and baptism are closely connected, it is not appropriate for an infant to be baptized since the infant is not capable of believing the gospel and repenting of his/her sins.