Water baptism is the first step of obedience in following Jesus after we have repented of our sins and committed to following Jesus. When a believer is submerged under water in the name of Jesus, it is a picture of the death and burial of Jesus Christ and results in our sins being washed away.
Acts 2:38 (NKJV)
38 Then Peter said to them, “Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit.
Acts 22:16 (NKJV)
16 And now why are you waiting? Arise and be baptized, and wash away your sins, calling on the name of the Lord.’