Believer’s Baptism is the act of being submerged in water as an acknowledgement of and participation with God’s saving and transformative work in the person. (Acts 10:47-48 and Romans 6:1-4). It is an intentionally public ceremony: an outward sign of the inward working of God’s grace in a person’s life. According to Scripture, the effect of God’s grace on an individual is like being born again, with a new life and identity in Christ.
Jesus himself explained this concept in his conversation with Nicodemus:
Jesus answered him, “Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God.” Nicodemus said to him, “How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?” Jesus answered, “Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. John 3:3-5
This truth was confirmed in the early Church:
Therefore, if anyone is in Christ, he [or she] is a new creation. The old has passed away; behold, the new has come. 2 Corinthians 5:17