Baptism by immersion in water by one having authority is the first saving ordinance of the gospel and is necessary for an individual to become a member of The Church of Jesus Christ of Latter-day Saints and to receive eternal salvation. All who seek eternal life must follow the example of the Savior by being baptized and receiving the gift of the Holy Ghost.
Baptism in the Lord's Way
The Savior revealed the true method of baptism to the Prophet Joseph Smith, making clear that the ordinance must be performed by one having priesthood authority and that it must be done by immersion:
"The person who is called of God and has authority from Jesus Christ to baptize, shall go down into the water with the person who has presented himself or herself for baptism, and shall say, calling him or her by name: Having been commissioned of Jesus Christ, I baptize you in the name of the Father, and of the Son, and of the Holy Ghost. Amen.
"Then shall he immerse him or her in the water, and come forth again out of the water" (D&C 20:73–74).
Immersion is symbolic of the death of a person's sinful life and the rebirth into a spiritual life, dedicated to the service of God and His children. It is also symbolic of death and resurrection. (See Romans 6:3–6.)
The Baptismal Covenant
Those who are baptized enter into a covenant with God to take upon themselves the name of Jesus Christ, keep His commandments, and serve Him to the end (see Mosiah 18:8–10; D&C 20:37). Church members renew this covenant each time they partake of the sacrament (see D&C 20:77, 79).
Those who keep the covenants they made at baptism are blessed by the Lord for their faithfulness. Some of the blessings include the constant companionship of the Holy Ghost, the remission of sins, and the privilege of being spiritually reborn. If they continue faithfully, they are promised eternal life (see 2 Nephi 31:19–20).
Little Children and Baptism
From latter-day revelation, we know that little children are redeemed through the mercy of Jesus Christ. The Lord said, "They cannot sin, for power is not given unto Satan to tempt little children, until they begin to become accountable before me" (see D&C 29:46–47). They are not to be baptized until they reach the age of accountability, which the Lord has revealed to be eight years of age (see D&C 68:27; Joseph Smith Translation, Genesis 17:11). Anyone who claims that little children need baptism "denieth the mercies of Christ, and setteth at naught the atonement of him and the power of his redemption" (Moroni 8:20; see also verses 8–19, 21–24).