The Catholic Church is the Body of Christ, the visible sign of an invisible reality – God’s salvific work in the world. The average layman, to the pope, to the newly baptized baby are the same amount Catholic. In fact, if only one Catholic remained alive on earth, the whole Church would exist. Thus, the Church is the Body of Christ, not in the same way as the Eucharist, but in a mystical way. “The Church is this Body of which Christ is the head: she lives from him, in him, and for him; he lives with her and in her” (CCC 807). The Church is also the Bride of Christ because Christ wed Himself to the Church in a mystical way. Chirst “loved [the Church] and handed himself over for her. He has purified her by his blood and made her the fruitful mother of all God’s children” (CCC 808). She receives the Word of God, and gives it to the world for their salvation. Christ is the Bridegroom, meaning that He will defend His bride, the Church, with His life, as He did on Calvary (Is 62:5, Jn 3:29, Mt 9:14-15).
But while the Church is the Body of Christ, not all Catholics make up the teaching authority of the Church. The teaching office of the Church is called the magisterium, which is composed of all the bishops of the Church. The Church cannot err in the matters of faith and morals, but that does not mean that individual Catholics cannot err in these matters, even including bishops. The only time that these bishops teach infallibly is when all the bishops agree in unison on a matter of faith or morals (matters of belief in God or matters of how one ought to act).
The ordinary magisterium describes when the bishops teach in unison on a matter of faith or morals. The solemn or extraordinary magisterium (rarely used) describes when the pope defines ex cathedra (“from the chair”) some infallible truth which is binding on all Catholics in the highest degree. Such definitions are called dogmas. This happens so rarely that the last time the Church infallibly defined something was in 1950, when she defined the dogma of the Assumption; before that, the Immaculate Conception in 1854.
The Church is on the defense in these claims, for to disprove her authority, all one would have to do is to disprove one teaching the Church claims is infallible. People have tried over the centuries to disprove her claim to authority, but have failed as often as they have tried, for, the Holy Spirit truly guides the Church, protecting her from error.
This truth does not mean that even the pope himself cannot be grave sinners. The Church’s authority exists outside of individuals, and in Christ. Christ is the Head of the Church. The pope does not replace Him, nor does he usurp or diminish Christ’s authority. In fact, by his office, the pope is a visible reminder of Christ on earth – one of the popes papal titles is the “Vicar of Christ.” His role in the Church means that he has an especial responsibility to live like Christ, but His papal authority does not rely on his personal relationship with Christ.
Some people will admit that Christ established a Church, but assert that the Church has since fallen into error, and thus that she (the Church) is no longer the one, true Church. But Christ promised to remain with His Church to the end of time, when He said that the “gates of hell shall not prevail against it” (Mt 16:18). We shall address this in further detail in later sections, but it is necessary for us to recognize that Christ established the Catholic Church and promised to remain with her to the end of time, and so if the Church has erred, so has Christ.
Now, it is easy to make all these lavish claims about the Catholic Church and her authority, but what reason do we have for doing so? Likewise, how can the Church know all she claims to know? For example, the Church teaches much more about God than that He is merely the Unmoved Mover or the Uncaused Cause. The only reason she can teach these things is because God revealed them to her, through Jesus Christ, and gave her the authority to teach these truths.
In the previous question’s answers, we addressed some of the basics of how far using pure reason can get us to understanding Who God is. But reason cannot determine that God is Three Divine Persons, yet one God; that the Second Person of that Trinity became flesh and died for our sake, to save us from our sin, etc.
When we say that the Church can only teach more advanced truths about God because He revealed them to her, we are saying that the Church only teaches in light of “Divine Revelation.” While many people throughout history have had significant revelations, for example, when Our Lady appeared to St. Juan Diego in Guadalupe, Mexico, or when in this last century, our Lord appeared to St. Faustina in Poland on multiple occasions, the Church does not incorporate even the slightest of truths expounded in these private revelations into doctrine. The Church has approved many apparitions and miracles, but her authority to do so and the criteria she uses in making these decisions only comes from Divine Revelation.
Divine, or Public, Revelation consists of all the truths which the Lord revealed through the patriarchs and prophets, culminating in His Son, Jesus Christ, and ending with the death of the last apostle. The Church, therefore, only teaches authoritatively based on the word of God, which the Lord reveals through Sacred Scripture and Sacred Tradition. Combined, these sources constitute the Deposit of Faith. No one can add anything to the material the Church uses to teach, because God stopped revealing this type of material with the death of the last apostle.
Even though we cannot see God, we see His effects – the miraculous recovery from disease, a man’s change of heart, perseverance against great odds. Likewise, though we cannot see Divine Revelation, we see its effects – the sacraments, religious orders, etc. Indeed, the Church is a product of Divine Revelation. “You are Peter, and upon this rock I will build my Church, and the gates of hell shall not prevail against it” (Mt 16:18).
Sacred Scripture constitutes the Bible, both Old and New testaments. Sacred Tradition is the living out of revelation, which we do in our own lives. It is the continuation of the oral transmission of the Gospel message. Scripture and Tradition never conflict because the authentic carrying out of something cannot conflict with that something. Instead, they complement each other, and serve as sources through which God transmits truths to the Church, and the Church to the world.