God has set many signs on the earth, as well as in the heavens; for instance, the oak of the forest, the fruit of the tree, the herb of the field, all bear a sign that seed hath been planted there....
Upon the same principle do I contend that baptism is a sign ordained of God, for the believer in Christ to take upon himself in order to enter into the kingdom of God....
Baptism is a sign to God, to angels, and to heaven that we do the will of God, and there is no other way beneath the heavens whereby God hath ordained for man to come to Him to be saved, and enter into the Kingdom of God, except faith in Jesus Christ, repentance, and baptism for the remission of sins, and any other course is in vain; then you have the promise of the gift of the Holy Ghost.
(Joseph Smith, Teachings, P. 198.)