When John the baptiser started his ministry he asked people to repent from their sins and get baptised as a mark of their repentance (Mk.1:4). He was insistent that only those who had genuinely repented should get baptised, saying that they should show the marks of repentance in action (Mt.3:7,8).
But the water baptism that Jesus brought was different! This became clear only after He had died and been brought back to life. It was only then that people could truly experience salvation, beginning with the forgiveness of their sins (Ez.36:25), and regeneration in their spirit by the work of the Holy Spirit by which God's laws began to be written into their heart and mind (vv.26,27). In other words, they would be born again (Jn.3:3). It was such people who could then illustrate by water baptism what God had done in their lives – their old life of sin having been put away and their beginning to experience the new life with a desire not to sin but to do the will of God in their life. That is what baptism signifies, by burying the old life in the water and the new person coming out from death to a new life (Ro.6:4). It is clear that only those who have repented from their sins, put their trust in Jesus as their Saviour from sins and then been born again can go through baptism meaningfully.
It is also clear that only immersing a person under water and bringing him out of it can represent this symbolism. But the debate among Christians is not only about the form but about baptising infants versus adults. If we understand the meaning of baptism we can see that it is not about infants versus adults but about baptising only those who have experienced true regeneration through repentance and faith in Jesus.
Many seem to consider getting baptised as one of the steps for getting accepted by God, among reading the Bible, praying, attending church, etc. Then baptism becomes another 'work' to make oneself acceptable to God. No, this is only for those who have already been accepted by grace through faith in Jesus (Ep.2:8).
Thus we ought to know the difference between the baptisms taught by John and Jesus. The apostle Paul was clear about this, so much so that he baptised those who had been baptised with John's baptism 'again' in the name of Jesus after making sure that they had come to trust in Him as their Saviour (Ac.19:3,4). The usual sequence the takes place in salvation is – a person hears the Gospel of Jesus, repents from his sins, puts his trust in Jesus for salvation from sins, gets baptised in water, and then gets baptised with the Holy Spirit (v.6).
It is true that many people in those early days got baptised in the name of Jesus without understanding its meaning or significance. For them it was only a matter of obedience to Jesus (Mt.28:19,20). But now we who have the advantage of having the Bible with us can do things with understanding. Religion follows rituals but a spiritual person can do things meaningfully and rightly.