From the earliest days of the church, baptism has been the visible sign and public witness that an individual has become a Christian. It is a means of demonstrating to others that a person has accepted Jesus as their Saviour and a declaration of their intention to follow Jesus wholeheartedly.
Jesus commanded baptism
When a Cristian is baptised they are obeying Jesus. Jesus said to His disciples "All authority in heaven and on earth has been given to me. Therefore go and make disciples of all nations, baptising them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you"
(Matthew 28:18-20)
Jesus himself was baptised
Jesus was baptised, not because he needed forgiveness, but out of obedience to God. When you are baptised, you identify with the obedience of Jesus. Jesus asked John the Baptist to baptise Him saying “ Let it be so now; it is proper for us to do this to fulfil all righteousness.”
(Matthew 3:15)
The Apostles taught Baptism
New believers need to be baptised. Peter made this plain at Pentecost,when he preached "Repent and be baptised, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit."
(Acts 2:38)
The first believers were baptised
3000 new Christians were baptised after Peters first sermon (Acts 2:41). Philip baptised believers in Samaria (Acts 8:12) and the Ethiopian official (Acts 8:38). Paul was baptised after his conversion (Acts 9:18) as was anyone who became a Christian in the New Testament (Acts 16:15,33).