But he cannot err when he is *in cathedra *, that is, when he intends to make an instruction and decree for the guidance of the whole Church, when he means to confirm his brethren as supreme pastor, and to conduct them into the pastures of the faith. For then it is not so much man who determines, resolves, and defines as it is the Blessed Holy Spirit by man, which Spirit, according to the promise made by Our Lord to the Apostles, teaches all truth to the Church, and, as the Greek says and the Church seems to understand in a collect of Pentecost, conducts and directs his Church into all truth: *But when that Spirit of truth shall come, he will teach you all truth *or, will lead you into all truth (John xvi. 13). And how does the Holy Spirit lead the Church except by the ministry and office of preachers and pastors? But if the pastors have pastors they must also follow them, as all must follow him who is the supreme pastor, by whose ministry Our God wills to lead not only the lambs and little sheep, but the sheep and mothers of lambs; that is, not the people only but also the other pastors: he succeeds S. Peter, who received this charge: Feed my sheep. Thus it is that God leads his Church into the pastures of his Holy Word, and in the exposition of this he who seeks the truth under other leading loses it. The Holy Spirit is the leader of the Church, he leads it by its pastor, he therefore who follows not the pastor follows not the Holy Spirit.