Baptism is an important rite that exists across all Christian traditions. In many, but not all, Christian churches, baptism is the act that admits the participant to membership in the church.
"Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God".Because of this, infants are baptized a few weeks after being born. In the Catholic ritual, water is poured over the head of the child while the priest repeats the baptismal formula of Matthew 28:19--
"I baptize you (name) in the Name of the Father, and of the Son, and of the Holy Spirit. Amen."Adult converts to Catholicism are immersed in water for baptism during the Easter vigil.
The significance and mode of baptism remain controversial subjects among evangelical Protestant Christians. Some churches believe that baptism needs to take place as an infant (called pedobaptism or in an alternate spelling paedobaptism), while others believe only when a person makes an informed decision for Christ should he be baptized. The latter position is called believers' baptism, and those who follow it cite the following Bible passage in support:
And as they went on [their] way, they came unto a certain water: and the eunuch said, See, [here is] water; what doth hinder me to be baptized? And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, I believe that Jesus Christ is the Son of God. Acts 8:36-37 (KJV)
In some churches, the water in John 3:5 is assumed to be the waters of birth and being born again refers to spiritual renewal. Thus baptism becomes an ordinance performed after conversion.
Baptists recognize baptism only by immersion and after conversion. The theologian L. L. Clover explains this position in his book The Church: Her Origin, Purpose, Doctrine, and History Baptists consider baptism one of two church ordinances, along with communion, usually known as the Lord's Supper. Baptists consider baptism as the individual believer's commitment to the acceptance of personal faith in Christ. They treat communion as a memorial service commemorating the death, burial, and resurrection of Jesus Christ.
In the Lutheran and Anglican churches, infant baptism by pouring is the norm. Among Christians of the Reformed tradition, including Presbyterians and others who hold to the Westminster Confession of Faith, baptism is administered to both believing adults and the children of a believer, for a public confession and as a sign and seal of God's Covenant of Grace.  It is properly administered by dipping, sprinkling or pouring, but is not essential for salvation.  Prominent past theologians have taught this doctrine such as John Calvin , as well as contemporary teachers such as R.C. Sproul 
Among those typically identified with the Anabaptist tradition, the Restoration Movement (seen by its adherents as a "restoration" to first century Christianity), and the Pentecostal churches, it is widely held that baptism is necessary in establishing a relationship with God. They practice baptism by full immersion in water, usually accompanied by an audible confession of faith. Such Christians believe it evident that in first century Christianity, as recorded in the book of Acts, baptism was ubiquitous. It is said that, "Of the eleven major conversion accounts in Acts, baptism is explicitly included in ten and never excluded (either explicitly or implicitly)."
Biblical accounts of baptism, with some degree of detail, often include phrases describing the person(s) as going into or coming out of water. This, along with the biblical comparison of baptism to burial, is part of their contention that the early Church practiced full immersion. The word itself, however, can mean either immersion, dipping (in water), or washing, and among Christians who baptise by pouring or sprinkling, it is believed that the wording in Matthew's Gospel that Jesus "went straighway out of the water," (per the King James Version) means only that he ascended the banks of the Jordan River following his baptism.
- The Westminster Confession of Faith for study classes by G.I.Williamson, 1964, pp207ff
- Institutes of the Christian Religion, John Calvin, 1536, trans. 1989, pp.512ff
- Now, That's a Good Question!, R.C.Sproul, 1996, p124-5, 339-342,