Baptism was adopted by John the Baptist as part of his messianic movement and has been a part of Christianity from the beginning as recorded in Acts of the Apostles and the Pauline letters. Early Christian baptism was by immersion, although there is debate if it was full or partial immersion. At this time, catechesis or instruction in the faith generally occurred after baptism. By the third and fourth century, as various heresies and false teachings arose, a period of catechesis preceded baptism. Also at this time, baptism began to be associated with Easter, with most baptisms taking place at the Easter Vigil. Postponement of baptism became more common during this period, with many waiting until shortly before their death to become baptized.
In the early Middle Ages, following the teachings of St. Augustine, an emphasis on the necessity of baptism for salvation became common and questions arose about what happened to those who died without being baptized. Throughout the sixth, seventh and eighth centuries, the rite became more simplified. As fewer of those being baptized were converts, pre-baptismal catechesis was abandoned and infant baptism became common.
The Church teaches that baptism is a requirement for salvation. It is the sacrament of initiation which brings the baptized into the life of the Children of God by configuring the person to Christ and obliging the Christian to share in the Church’s apostolic and missionary activity. The Church recognizes three types of baptism: sacramental baptism, baptism of desire (an explicit or implicit desire to be part of the Church founded by Jesus) and baptism of blood (martyrdom). It is an actual supernatural transformation with parallels to Noah and the flood and the passage of the Israelites through the Red Sea. It represents both a cleansing of original sin and a dying and rising with Christ.
There are four conditions for a baptism to be valid: use of the verb baptism; use of the Trinitarian formula, baptizing in the name of the Father, Son and Holy Spirit; use of water; and the intention of the celebrant to actually perform a baptism. As long as these conditions are met, the Church recognizes a baptism as valid, regardless of which denomination performed the baptism. Since baptism imparts an indelible seal upon the soul, baptism cannot be repeated. In the Catholic Church, the ordinary minister of baptism is a bishop, priest or deacon, with administration generally entrusted to the parish priest. However, in a case of necessity, defined as imminent danger of death, any person, regardless of religion, may baptize provided they have the intention to perform a Christian baptism.