Abstract of Leo XIII Satis cognitum
1. Unity, characteristic of the Church founded by Christ, has a strong influence on souls. The conditions for the return of Protestants are established by God, not by men.
2. Both in the natural and in the supernatural order, God makes use of men to serve men. So Jesus Christ has perpetuated His mission in the Catholic Church, which is both spiritual and visible. That external element is essential to the life of the Church, which is simply the living mystical Body of Christ. The physical Christ the Head is the principle of the supernatural life that animates the Church.
Two errors: (1) Some affirm exclusively the spiritual nature of the Church; (2) some deny any supernatural element. Christ is a person with two natures. The Church is a society which is both supernatural and exterior at the same time. This twofold element will last for the life of the Church. To determine the nature of the Church, we must investigate what Christ wanted and did.