Two of his books have been very edifying to me. One is his Introduction to the Devout Life. The other is now published under the title: The Catholic Controversy: St. Francis de Sales' Defense of the Faith.
The latter book was written in the form of pamphlets to the Calvinists of the Chablais region of France, south of Geneva. He did not originally intend to write these pamphlets. As he went from house to house to talk with the Calvinists, they repeatedly refused to talk with him or even listen to him. So he started writing the pamphlets, and distributed them under doors in the villages and towns. Through his work in this region over the course of four years (from 1594 to 1598), 72,000 Calvinists were brought back into the Catholic Church.
One of the most important points in these pamphlets is that the Church comes from the Apostles, as the Apostles come from Christ, and as Christ comes from the Father. The Father sent the Son. The Son authorized and commissioned the Apostles. The Apostles authorized and commissioned the bishops. And these bishops authorized and commissioned bishops. This is a top-down transmission of divine authority, from the Father, through the Son, through the Apostles, and through the bishops. Only those sent by the Apostles should be received by Christians, and thus only those sent by the bishops sent by the Apostles should be received by the Christians. We should not follow those who are self-sent, or self-appointed, for they are not authorized by Christ to shepherd the Lord's sheep. Anyone can claim to be authorized, but only those who have been appointed by those whom the Apostles sent are actually authorized. In this way the unity of the Church flows directly from the unity of Christ Himself; just as an organism grows, the Church retains within itself the unity it received directly from the incarnate Christ, its Head. "We are to grow up in all aspects into Him, who is the head, even Christ from whom the whole body, being fitted and held together by that which every joint supplies ...." (Ephesians 4:16)
Recently I wrote, "I think there are two fundamentally different ways of trying to find the Church. One compares form, the other traces matter. As far as I can tell, one of those two ways must take priority." Comparing form (i.e. comparing one's own interpretation of Scripture to the various denominations' statements of faith, and finding the closest fit) is a method that is intrinsically disposed to disunity. The divisions that arise by way of that method are interminable if sought to be removed by that method. That is because the method itself is a large part of the cause of the division. The method carries with it an implicit assumption that there is no authoritative interpretation, no magisterium. That is the significance of this statement by Tertullian and this statement by St. Vincent of Lerins. When the Apostles were alive, their interpretation of their own writings was the authoritative interpretation. And from the first generation after the Apostles, the Church has always believed that the authoritative interpretation belonged to those whom the Apostles appointed (i.e. the bishops). The "compare form" way of finding the Church leaves out the matter; it de-materializes the Church. In that way, it de-materializes the 'joints' that connect each member to Christ the Head.
So if comparing form is not the way to find the Church, then what does it mean to "trace matter"? The sacramental successions, from bishop to bishop all the way back to the Apostles and through the Apostles to Christ, are the material 'joints' that connect us to Christ. That is why the unity of the Church (i.e. the Body) depends on finding and following only those bishops who have this succession, i.e. are connected by these joints all the way back to the Apostles. This is why recognizing the nature and importance of Apostolic succession is essential for ecumenical unity. Recently, in this conversation, a Protestant named John asked me the following question: "How do you identify the true church?" In reply I wrote something that I would write to any Protestant:
We identify the true Church by going back to Jesus. We know that Jesus founded a Church. Now the key is to keep your finger on that thing that Jesus founded, and move forward through history, century by century, until you reach the present day. Don't go quickly. Read the writings of the fathers of the first century, then the second century, and then third century, and then the fourth century, and then the fifth century. Now, whenever there is a schism, you have to determine which is the split off (at least in some respect), and which is the continuation of the Church that Christ founded. How did the fathers determine which is the continuation of the Church Christ founded, and which is the schism from that Church? Notice the roles of the Ecumenical Councils. Notice also the role of the Pope in the authority of the Ecumenical Councils. (I'm not trying to be patronizing in this paragraph -- I'm simply laying out how I think the true Church is to be found. I'd be interested in how you agree/disagree with that general methodology, and where in history our 'fingers' part ways, so to speak, and at that very point where our fingers part ways, why your finger goes away from mine.)The only way, in my opinion, for all Christians to be reunited in one Body is to retrace our steps conceptually to the various points in history at which we came apart. Then we need to dialogue about the principled way by which, in every case in which there is a schism of some sort, we can determine which is the "schism from" the true Church, and which is the continuation of the true Church.
I stood in front of the bust (in the photo above) this morning before mass, and asked St. Francis to pray for us, that we might be made one in the truth, and in the love of the truth. May we have a double portion of his passion to reconcile all souls with Christ, by reconciling them with Christ's Body, the Church. Lord Jesus, we need Your help. We need You to help us to be truly united as You desire us to be. Help us Lord to find and unite to the true shepherds that You have appointed. And help us Lord to love our brothers and sisters in Christ, with such love that we seek out and hold on to true unity, and ward off all attacks against our unity. In the name of the Father, and of the Son, and of the Holy Spirit. Amen.