Baptism is a promise to God that you will live according to your sincere understanding of God in all things:
...to stand as witnesses of God at all times and in all things, and in all places that ye may be in, even until death... (Mosiah 18:9)
This means to live in accordance with your conscience, or your view of the ideal human, in all things, at all costs, until you die:
And we are willing to enter into a covenant with our God to do his will, and to be obedient to his commandments in all things that he shall command us, all the remainder of our days.... (Mosiah 5:5)
Baptism is a commandment, and it is required for salvation:
And again I say unto you, ye must repent, and be baptized in my name, and become as a little child, or ye can in nowise inherit the kingdom of God. (3 Nephi 11:38)
23 And he commandeth all men that they must repent, and be baptized in his name, having perfect faith in the Holy One of Israel, or they cannot be saved in the kingdom of God.
24 And if they will not repent and believe in his name, and be baptized in his name, and endure to the end, they must be damned; for the Lord God, the Holy One of Israel, has spoken it. (2 Nephi 9)
The Lord himself was baptized during his mortal ministry, showing the world that it is a requirement:
9 And again, it showeth unto the children of men the straitness of the path, and the narrowness of the gate, 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. (2 Nephi 31)
The Lord said we are to follow his example: [TODOOO]
`Verily, verily, I say unto you, this is my gospel...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; (3 Nephi 27:21)`
Baptism is an essential part of repentance. You can’t repent completely without being baptized:
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. (Alma 7:15)