Jesus told Nicodemus that “except a man be born of water and the spirit, he cannot enter the kingdom of heaven.”[i] What is being born of the Spirit? John the Baptist said of this process of being purified by the fire of the Holy Ghost:
“I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and with fire:”[ii]
When the apostles in Acts found some disciples in Samaria who had only been baptized, they sent apostles to give them the gift of the Holy Ghost:
“Now when the apostles which were at Jerusalem heard that Samaria had received the word of God, they sent unto them Peter and John: Who, when they were come down, prayed for them, that they might receive the Holy Ghost: (For as yet he was fallen upon none of them: only they were baptized in the name of the Lord Jesus.) Then laid they their hands on them, and they received the Holy Ghost.”[iii]
So here we see the necessity of not only being cleansed though baptism but also through being born of the Spirit or receiving the Holy Ghost.
“Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.”[iv]
John the Baptist’s equating of the gift of the Holy Ghost with a baptism or purifying by fire is mentioned in several other scriptures:
“For the gate by which ye should enter is repentance and baptism by water; and then cometh a remission of your sins by fire and by the Holy Ghost.”[v]
“Jesus said to the Nephites: “after that ye are baptized with water, behold, I will baptize you with fire and with the Holy Ghost”[vi]
Lastly, the testifying that Jesus is the Christ is one of the gifts of the Holy Ghost:
“Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed: and that no man can say that Jesus is the Lord, but by the Holy Ghost.”[vii]
[i] John 3:5
[ii] Matthew 3:11
[iii] Acts 8:14-17
[iv] Acts 2:38
[v] 2 Nephi 31:17 see also D&C 19:31 for more on equating the Holy Ghost to purifying fire.
[vi] 3 Nephi 12:1
[vii] 1 Corinthians 12:3