Baptism is a water purification ritual practiced in certain religions such as Christianity, Mandaeanism, and Sikhism, and has its origins with the Jewish ritual of mikvah. The word baptize derives from the Greek word ??????? (the infinitive; also listed as the 1st person singular present active indicative ???????), which loosely means "to dip, bathe, or wash". To some groups it is a matter of religious conviction to assert that baptism is precisely equivalent to, to plunge something entirely into the water, so that the water closes over it.
Today, baptism is most readily identified with Christianity, where it symbolizes the cleansing (remission) of sins, and the union of the believer with Christ in His death, burial and resurrection so that he becomes one of Christ's Faithful. The Christian ritual of baptism traces back to the baptism of Jesus by John the Baptist, who the Bible says baptized Jesus in the Jordan River. Baptism among Christians is performed by aspersion (sprinkling water over the head), infusion (pouring water over the head) or full immersion (lowering the entire body into a pool of water). The choice to be baptized is made by a confessing believer (believer baptism, or credobaptism), regardless of age, as a confession of his faith; or on behalf of the child by his or her parents (paedobaptism) if the parents have themselves been baptized, and profess faith. Some churches practice credobaptism and some practice paedobaptism and some churches practice both. Some practice immersion, some practice pouring, and some practice sprinkling. There are differences in views about the nature and practice of Christian baptism.
Martin Luther, for example, placed great importance on baptism. Luther states in The Large Catechism of 1529,"To put it most simply, the power, effect, benefit, fruit, and purpose of Baptism is to save. No one is baptized in order to become a prince, but as the words say, to 'be saved.' To be saved, we know, is nothing else than to be delivered from sin, death, and the devil and to enter into the kingdom of Christ and live with him forever."
In contrast, Baptist groups deny that baptism has any such power, but rather only testifies outwardly to the operation of God's power, which is invisible, internal, and completely separate from the rite itself.
For Christians who baptize by pouring or sprinkling, the washing with water from above pictures the cleansing of one's sins by the blood of Christ, by the Holy Spirit, who unites the baptized person to Christ in his death and his resurrection from the dead. It is administered from above to point to that gift of the life-giving Spirit, and to portray baptism as an act not of man but of God. In contrast, a person baptized by immersion is enclosed under the water and brought out, to signify cleansing through death and burial with Christ, and consequent raising again in newness of life by the Holy Spirit. Baptism is a public rite, in testimony to others of the grace of God bestowed upon the person, and as a seal of God's promises in Christ to those who believe.