The Sacrament of Baptism is often called "The door of the Church," because it is the first of the seven sacraments not only in time (since most Catholics receive it as infants) but in priority, since the reception of the other sacraments depends on it. It is the first of the three Sacraments of Initiation, the other two being theSacrament of Confirmation and the Sacrament of Holy Communion. Once baptized, a person becomes a member of the Church. Traditionally, the rite (or ceremony) of baptism was held outside the doors of the main part of the church, to signify this fact.

Christ Himself ordered His disciples to preach the Gospel to all nations and to baptize those who accept the message of the Gospel. In His encounter with Nicodemus (John 3:1-21), Christ made it clear that baptism was necessary for salvation: "Amen, amen I say to thee, unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God." For Catholics, the sacrament is not a mere formality; it is the very mark of a Christian, because it brings us into new life in Christ.

That doesn't mean that only those who have been formally baptized can be saved. From very early on, the Church recognized that there are two other types of baptism besides the baptism of water.

The baptism of desire applies both to those who, while wishing to be baptized, die before receiving the sacrament and "Those who, through no fault of their own, do not know the Gospel of Christ or His Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do His will as they know it through the dictates of conscience" (Constitution on the Church, Second Vatican Council).

The baptism of blood is similar to the baptism of desire. It refers to the martyrdom of those believers who were killed for the faith before they had a chance to be baptized. This was a common occurrence in the early centuries of the Church, but also in later times in missionary lands. The baptism of blood has the same effects as the baptism of water.

While the Church has an extended rite of Baptism which is normally celebrated, which includes roles for both parents and godparents, the essentials of that rite are two: the pouring of water over the head of the person to be baptized (or the immersion of the person in water); and the words "I baptize you in the name of the Father, and of the Son, and of the Holy Spirit."

Since the form of baptism requires just the water and the words, the sacrament, like theSacrament of Marriage, does not require a priest; any baptized person can baptize another. In fact, when the life of a person is in danger, even a non-baptized person—including someone who does not himself believe in Christ—can baptize, provided that the person performing the baptism follows the form of baptism and intends, by the baptism, to do what the Church does—in other words, to bring the person being baptized into the fullness of the Church.

In both cases, a priest may later perform a conditional baptism.

In the Catholic Church today, baptism is most commonly administered to infants. While some other Christians strenuously object to infant baptism, believing that baptism requires assent on the part of the person being baptized, the Eastern Orthodox, Anglicans, Lutherans, and other mainline Protestants also practice infant baptism, and there is evidence that it was practiced from the earliest days of the Church.

Since baptism removes both the guilt and the punishment due to Original Sin, delaying baptism until a child can understand the sacrament may put the child's salvation in danger, should he die unbaptized.

Adult converts to Catholicism also receive the sacrament, unless they have already received a Christian baptism. (If there is any doubt about whether an adult has already been baptized, the priest will perform a conditional baptism.) A person can only be baptized once as a Christian—if, say, he was baptized as a Lutheran, he cannot be rebaptized when he converts to Catholicism.

While an adult can be baptized after proper instruction in the Faith, adult baptism normally occurs today as part of the Rite of Christian Initiation for Adults (RCIA) and is immediately followed by Confirmation and Communion.

Baptism has six primary effects, which are all supernatural graces:

1. The removal of the guilt of both Original Sin (the sin imparted to all mankind by the Fall of Adam and Eve in the Garden of Eden) and personal sin (the sins that we have committed ourselves).
   
   
2. The remission of all punishment that we owe because of sin, both temporal (in this world and in Purgatory) and eternal (the punishment that we would suffer in hell).
   
   
3. The infusion of grace in the form of sanctifying grace (the life of God within us); the seven gifts of the Holy Spirit; and the three theological virtues.
   
   
4. Becoming a part of Christ.
   
   
5. Becoming a part of the Church, which is the Mystical Body of Christ on earth.
   
   
6. Enabling participation in the sacraments, the priesthood of all believers, and the growth in grace.