Rhetorical: As Mormon ties up the various threads, he makes a wonderful allusion to his earlier discussion of judging. He had discussed the nature of judging, and now he declares that he is judging his audience! Since he has said that one may judge if they have the Spirit of Christ, he certainly is claiming spiritual confirmation of this judgment and declaration. This is also a reprise of the “judgment” he declared in verse 4.
In this case, he judges them well. “I judge that ye have faith in Christ.” Mormon provides this statement as a benediction, but one with teeth in it, for he also declares “if ye have not faith in him then ye are not fit to be numbered among the people of his church.” If we are to be members of this church, faith is a requirement.
This is not to say, of course, that we must have a full or strong faith. As Alma taught in chapter 32, there are stages in the growth of our faith, and all stages are welcome and essential in the church. What Mormon is saying is that if we are to have a church that is based on Christ, then it is absolutely essential that we have faith in Christ. They cannot be separated.