As noted in verse 5, we may see here two “things” that constitute the sin of Corianton. The obvious one is being lead way after the harlots. The first listed, however, is that he was led away by a “vain or foolish thing.” Of course it is possible that the vain or foolish thing might be the same as the harlot, but it is doubtful. The more probable explanation would be that there is a different aspect of his sin described by the vain and foolish thing, and this must in some way describe his apostate state.
The last part of the verse is yet another sin compounding his personal sin. Because of his actions, he caused unbelief on the part of others. It is quite understandable that this should happen, as we are very aware that one person who does not live the gospel can make it difficult to teach the value of the gospel to others. Alma’s inability to assure his son’s orthodoxy was seen as a weakness in the doctrine, not rebelliousness in the person of Corianton. The Zoramites were able to use this as one of their excuses for not believing Alma.