Baptism

Baptism by immersion is the first saving ordinance of the gospel. It is the only way for a person to become a member of The Church of Jesus Christ of Latter-day Saints and have eternal salvation. Those who wish to obtain eternal life must follow the example of the Savior and be baptized to receive the gift of the Holy Ghost.
This ordinance must be performed by one who holds the priesthood.

4 Wherefore, I would that ye should remember that I have spoken unto you concerning that prophet which the Lord showed unto me, that should baptize the Lamb of God, which should take away the sins of the world.
5 And now, if the Lamb of God, he being holy, should have need to be baptized by water, to fulfil all righteousness, O then, how much more need have we, being unholy, to be baptized, yea, even by water!
6 And now, I would ask of you, my beloved brethren, wherein the Lamb of God did fulfil all righteousness in being baptized by water?
7 Know ye not that he was holy? But notwithstanding he being holy, he showeth unto the children of men that, according to the flesh he humbleth himself before the Father, and witnesseth unto the Father that he would be obedient unto him in keeping his commandments.
8 Wherefore, after he was baptized with water the Holy Ghost descended upon him in the form of a dove.
9 And again, it showeth unto the children of men the straitness of the path, and the narrowness of the agate, by which they should enter, he having set the example before them.
10 And he said unto the children of men: Follow thou me. Wherefore, my beloved brethren, can we follow Jesus save we shall be willing to keep the commandments of the Father?
11 And the Father said: Repent ye, repent ye, and be baptized in the name of my Beloved Son.
12 And also, the voice of the Son came unto me, saying: He that is baptized in my name, to him will the Father give the Holy Ghost, like unto me; wherefore, follow me, and do the things which ye have seen me do.
13 Wherefore, my beloved brethren, I know that if ye shall follow the Son, with full purpose of heart, acting no hypocrisy and no deception before God, but with real intent, repenting of your sins, witnessing unto the Father that ye are willing to take upon you the name of Christ, by baptism—yea, by following your Lord and your Savior down into the water, according to his word, behold, then shall ye receive the Holy Ghost; yea, then cometh the baptism of fire and of the Holy Ghost; and then can ye speak with the tongue of angels, and shout praises unto the Holy One of Israel.
2 Nephi 31:4–13

Baptism is a symbol of the death of a persons sinful life and the rebirth of a spiritual life. Those baptized take upon them the covenant and promise to take upon them the name of Christ, to keep his commandments, and serve Him until the end.

14 Now I say unto you that ye must repent, and be born again; for the Spirit saith if ye are not born again ye cannot inherit the kingdom of heaven; therefore come and be baptized unto repentance, that ye may be washed from your sins, that ye may have faith on the Lamb of God, who taketh away the sins of the world, who is mighty to save and to cleanse from all unrighteousness.
15 Yea, I say unto you come and fear not, and lay aside every sin, which easily doth beset you, which doth bind you down to destruction, yea, come and go forth, and show unto your God that ye are willing to repent of your sins and enter into a covenant with him to keep his commandments, and witness it unto him this day by going into the waters of baptism.
16 And whosoever doeth this, and keepeth the commandments of God from thenceforth, the same will remember that I say unto him, yea, he will remember that I have said unto him, he shall have eternal life, according to the testimony of the Holy Spirit, which testifieth in me.
Alma 7:14-16

Those who are baptized receive blessings, such as the constant companionship of the Holy Ghost, remission of sins and the privilege of being spiritually reborn.

All little children are redeemed through the mercy of Christ, therefore, do not need to be baptized until they are 8 years old. "They cannot sin, for power is not given unto Satan to tempt little children, until they begin to become accountable before me"
D&C 29:46-47

19 And no unclean thing can enter into his kingdom; therefore nothing entereth into his rest save it be those who have washed their garments in my blood, because of their faith, and the repentance of all their sins, and their faithfulness unto the end.
20 Now this is the commandment: Repent, all ye ends of the earth, and come unto me and be baptized in my name, that ye may be sanctified by the reception of the Holy Ghost, that ye may stand spotless before me at the last day.
21 Verily, verily, I say unto you, this is my gospel; and ye know the things that ye must do in my church; for the works which ye have seen me do that shall ye also do; for that which ye have seen me do even that shall ye do;
22 Therefore, if ye do these things blessed are ye, for ye shall be lifted up at the last day.
3 Nephi 27: 19-22

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

37 And again, by way of commandment to the church concerning the manner of baptism—All those who humble themselves before God, and desire to be baptized, and come forth with broken hearts and contrite spirits, and witness before the church that they have truly repented of all their sins, and are willing to take upon them the name of Jesus Christ, having a determination to serve him to the end, and truly manifest by their works that they have received of the Spirit of Christ unto the remission of their sins, shall be received by baptism into his church.
D&C 20:17


Scripture references: 2 Nephi 31:4–13, Alma 7:14-16, D&C 29:46-47, 3 Nephi 27: 19-22, Moroni 8:20, D&C 20:17