5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
This is the scripture mastery that our youth learn, but for our discussion now, it might be helpful to back up a few verses.
1 There was a man of the Pharisees, named Nicodemus, a ruler of the Jews:
2 The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him.
3 Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.
4 Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother’s womb, and be born?
This birth that Jesus spoke of was not the same as the birth of a baby. The birth Jesus spoke of is a spiritual birth. Baptism is symbolic of being "born again" spiritually.
Baptism is the gate by which we enter the kingdom of God. It is such an important ordinance that the Savior himself was baptized "to fulfill all righteousness". Being baptized by immersion is similar to being cleansed by bathing, but it is a spiritual cleansing. Baptism is what the Savior was speaking of when he said that a man must be born of the water.
But what about being born of the spirit? What was the Savior speaking of? After we are baptized by one holding the Priesthood of God, we are then confirmed a member of the church, and receive the gift of the Holy Ghost by the laying on of hands. The Holy Ghost gives us a baptism of spirit. When we receive this ordinance, we are then blessed to have the companionshop of the Holy Ghost, as long as we are worthy of it. The Prophet Joseph Smith taught: “You might as well baptize a bag of sand as a man, if not done in view of the remission of sins and getting of the Holy Ghost. Baptism by water is but half a baptism, and is good for nothing without the other half—that is, the baptism of the Holy Ghost." (History of the Church, 5:499).
Elder David Bednar said, "We were baptized by immersion in water for the remission of sins. We must also be baptized by and immersed in the Spirit of the Lord, “and then cometh a remission of your sins by fire and by the Holy Ghost” (2 Ne. 31:17). (From this talk)