John's baptism was a baptism of repentance. Christian baptism is for regeneration. Which is why the disciples of John the Baptist, in Acts 19, needed to receive Christian baptism. Both John's baptism and Christian baptism are of water, the difference is that John's baptism was for repentance in anticipation of the coming of the Messiah; Christ instituted a new baptism by which people--both Jew and Gentile--become Christian.
Repentance isn't a singular act in the life of the Christian, but a calling and way of life. We are called to confess our sins, and to die daily in repentance. Thus repentance is a chief mark of the Christian life. The Christian is a baptized person, trusting in Christ, and bearing the cross of repentance.
Therefore the infant who is brought to the waters of baptism is made a Christian, born anew by God's grace according to Christ's word and God's promise; repentance naturally will follow as the child is raised up in the faith. It may be that for some the seed will be choked out by thorns, or for some that the seed will be eaten by the birds, but the seed is not made ineffective by thorns or birds, it takes root and grows--which is why the Church does not merely baptize and stand back or preach the Word once and stand back but brings the life-giving Word and Sacrament by the faithful command of Christ. St. Paul telling St. Timothy as a pastor to "preach the Gospel in and out of season".
-CryptoLutheran
