Originally posted by Contra_Mundum
Paul's not talking about a special class of Christians or "non-carnal" Christians, but of "spiritual persons," or persons led by the Spirit (only Christians fit the bill). The brother in the fault is a fellow church-member, and it's highly likely that he too is a genuine Christian, but he's not walking by the Spirit, walking in his sin. He needs restoration to the path of life.
As for the related issue of carnality, a person living habitually in sin is either not a Christian at all, or he is living as if he were an unsaved person, a truly shocking condition that Paul addresses with outrage in 1 Cor. 3:1-4, He addresses them as though they have made zero progress in sanctification, the "putting off of the flesh," and they are still almost entirely "fleshly." See esp. v. 4, "For when one [does thus] and another [thus], ARE YOU NOT MEN?" i.e. You're acting like unsaved people! Knock it off!