“By the power of the Holy Ghost—who is the Sanctifier (3 Ne. 27:19–21)—dross, iniquity, carnality, sensuality, and every evil thing is burned out of the repentant soul as if by fire; the cleansed person becomes literally a new creature of the Holy Ghost. (Mosiah 27:24–26.) He is born again.
“The baptism of fire is not something in addition to the receipt of the Holy Ghost; rather, it is the actual enjoyment of the gift which is offered by the laying on of hands at the time of baptism. ‘Remission of sins, ’ the Lord says, comes‘by baptism and by fire, yea, even the Holy Ghost.’ (D. & C. 19:31; 2 Ne. 31:17.) Those who receive the baptism of fire are ‘filled as if with fire.’ (Hela. 5:45.)”
(Mormon Doctrine, p. 73).