Faith in Christ, and faith in the Body of Christ (i.e. the Church), cannot be separated. One cannot have one without the other, without some degree of self-deception or Nestorianism. That is because the Son of God became man. If we are not to be ecclesial deists, what are we to be? The same person who said, "Lord, to whom shall we go? You have the words of eternal life.", is the person to whom we must cling. If we want to be where Christ is, we must be where Peter is. Between 374 and 379 AD, St. Jerome wrote the following to Pope Damasus I (366-383):
My words are spoken to the successor of the fisherman, to the disciple of the cross. As I follow no leader save Christ, so I communicate with none but your blessedness, that is with the chair of Peter. For this, I know, is the rock on which the church is built! This is the house where alone the paschal lamb can be rightly eaten. This is the ark of Noah, and he who is not found in it shall perish when the flood prevails. ... The church here [i.e. Syria] is rent into three factions, and each of these is eager to seize me for its own. .... I meantime keep crying: "He who clings to the chair of Peter is accepted by me... Therefore I implore your blessedness, by our Lord's cross and passion, ..... to give an apostolic decision. Only tell me by letter with whom I am to communicate in Syria.
Trading sacramentally grounded authority for doctrinally grounded authority is a concession to a kind of gnosticism that 'de-materializes' [i.e. abstracts away the matter] the ground or basis of magisterial authority, and in doing so denies the enfleshment of God in the incarnation. Gnosticism is, in my opinion, at the root of all heresy, as I have argued here. That is because gnosticism is the antithesis of the heart of the gospel, that God became man. We should not be surprised, therefore, to find this antithesis of the gospel at the root of every heresy. At that link I argue that Peter's role as the Church's visible principle of unity becomes more understandable the more we explore the implications of the incarnation.