The practice of baptism by complete immersion did not begin in Christ’s mortal ministry (see Moses 6:64; Mosiah 18:14-16), but its rich symbolism is based on the death, burial, and resurrection of Christ. In the Old World, Paul spoke often of the spiritual symbols associated with immersion (e.g., see Romans 6:3-6; Colossians 2:12).
While we have no recorded teaching of this symbolism in the Book of Mormon, the ancient Nephites undoubtedly had been taught and understood it. Perhaps it was once again taught by the Savior himself as he now instructed them concerning the manner of baptism.
“Thou Art a Sober Child”
It should not be thought that Mormon was somber; rather, he was sober—meaning that he was thoughtful and serious-minded, mature beyond his chronological age. Undoubtedly Mormon’s soberness was as much spiritual as emotional. The things of the Lord were important to him even at such an early age, as evidenced by the visitation of the Lord to him (see verse 15).