Joseph Smith

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. The Savior says, ‘Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.’ [John 3:5.]”

Joseph Smith, History of the Church, 5:499

Bruce R. McConkie

Sins are remitted not in the waters of baptism, as we say in speaking figuratively, but when we receive the Holy Ghost.  It is the Holy Spirit of God that erases carnality and brings us into a state of righteousness.  We become clean when we actually receive the fellowship and companionship of the Holy Ghost.  ... The actual cleansing of the soul comes when the Holy Ghost is received.  The Holy Ghost is a sanctifier whose divine commission is to burn dross and evil out of a human soul as though by fire.

Elder Bruce R. McConkie, New Witness for the Articles of Faith, p. 290, 239.