Peter said to them," Repent, and be baptized every one of you in the name of Jesus Christ so that your sins may be forgiven;, and you will receive the gift of the Holy Spirit."
Acts 2:38 (NRSV)
Just as the baptism represents the death, burial and resurrection of Jesus Christ, it symbolizes the death and burial of the old self of the repentant believer, and the joyous birth of a brand new being in Christ. Those who founded the Disciples movement taught baptism by immersion as the accepted form.
From the : "Word to the Church on Baptism," Commission on Theology, 1987
Baptism is a public act by which the church proclaims God’s grace, as revealed in the life, death, and resurrection of Jesus Christ, through the use of a visible sign of God’s gracious initiative and the human individual’s response in faith. With other Christians we affirm that baptism is at once a divine gift and a human response.
Baptism, as a gift of grace, received by faith, expresses its meaning in a variety of images: new birth; a washing with water; a cleansing from sin; a sign of God’s forgiving grace; the power of new life now and the pledge of life in the age to come. The meaning of baptism is grounded in God’s redemptive action in Christ, it incorporates the believer in the community in the body of Christ, and it anticipates life in the coming age when the powers of the old world will be overcome, and the purposes of God will triumph.
