Alma departs and is never seen again: “as to his death or burial we know not of.” Verse 19 suggests that Alma was “taken up by the Spirit, or buried by the hand of the Lord, even as Moses.” This statement appears to refer to Deuteronomy 34:5–6: “So Moses the servant of the Lord died there in the land of Moab, according to the word of the Lord. And he buried him in a valley in the land of Moab, over against Beth-peor: but no man knoweth of his sepulchre unto this day.”
Since no one knew what happened to him, they surmised that because Alma was a righteous man that his death would have been similar to another righteous man: Moses.