Jesus commands his disciples to go and make disciples of all nations baptising them in the name of the Father and the Son and the Holy Spirit. So one of the reasons to baptise is because Jesus told us to (Matthew 28:19). But the question arising from this is, what is the point of baptism? What does it actually achieve?
To answer this we need to understand what baptism actually meant to Jesus and his disciples at that time. There are many examples of baptism in the New Testament, and they all involve water (Mark 1:9, Acts 2:40, Acts 8:38) to mention just a few. The word baptise simply means to wash. So when the disciples baptised people they were in effect saying these people needed be washed clean. But what did they need to be clean from?
The fact that anyone needs to be washed means that in the first place that they are dirty. The truth is people are dirty, or sinful before God and therefore need to be washed clean (Romans 3). Water cannot make people clean before God, therefore God sent Jesus to wash away, or take away our sin, which has he did through his death and resurrection. So then all those who trust in Jesus have been made clean.
What baptism says is that we accept that we are dirty and need washing. Baptism acknowledges the fact we cannot wash ourselves of our sin and needed someone else to take away our sin, (that’s why baptism is always done by someone else). Baptism points to the fact that Jesus has done it for us in his death and resurrection.
It is important to realise that Baptism cannot make anyone right with God. It is only Jesus death and resurrection that makes us clean. But what baptism says is, we acknowledge our need to be made clean before others and Jesus, and accept Jesus as Lord. Baptism is an outward sign of an inward reality. By this I mean, though water does not take away our sin, the Holy Spirit does come into our lives and truly does by changing us to accept Jesus as Lord.
Just as a final note, though Jesus was baptised, he did not need to in order to make him free from sin, which John admits when he baptises Jesus (Matthew 3:13).