The source of authority in this context means that which has the authority to teach faith and morals to the world, specifically Christians or any would-be disciple of Christ.  The assumption here is that the teachings from an unchanging God are also unchanging.

The first part in McLean Bible Church’s Spiritual Bootcamp series from head pastor Lon Solomon is about the Reality of the Bible because, as he says in the sermon, all we know about God, Jesus, salvation, creation, et cetera, comes from and begins with the Bible.  And so, in that tradition, the Bible is the source of what we know and is our source of authority. That is why the inerrancy of the Bible is crucial, for to be in error, at any point, poses a problem: how can we trust the Bible as a source of authority if it has flaws? Evangelical Christians defend the inerrancy of the Bible as if their soul depends on it because, in that tradition, it does. One of the pillars of the Protestant Reformation is sola scriptura (scripture alone) and, so, the Bible’s place in authority is paramount. Consequently, if a particular doctrine cannot be discerned clearly in the pages of the Bible, it is suspect or false.

The Catholic Church source of authority is, rather conveniently, the Church itself or more specifically the magisterium— the authority represented by the present Pope and his bishops as well as all the church’s past teaching as a continuum traceable to Jesus first authorization of the first pope, Peter, in Matthew 23:18, commissioned as the rock on which Christ would build his Church.

Analysis

Protestant and Catholics actually agree that the Bible is authoritative.  The difference is, in the Protestant view, the Bible stands as authoritative in the hands of the believer guided by the Holy Spirit, whereas Catholics believe the Bible is authoritative in the hands of the Church guided by the Holy Spirit. After all, the Church was responsible for compiling the canon of scripture, so how is it that Protestants use the very thing composed by the Church as authoritative without recognizing the authority of the Church that compiled it?

And when one considers that there are numerous Protestants denominations of varying viewpoints but only one, holy, catholic and apostolic Church, which paradigm appears to be working? We tend to read the Bible through the lens of our personal experience, culture, language, politics and desires. So what really is the source of authority? Is it the Holy Spirit, a false spirit, or ourselves?

Catholic teaching is remarkably, almost miraculously, stable. Teachings that many mainstream Protestant denominations once held to be true have been eventually warped or disregarded including teachings on birth control, sexuality, marriage, divorce, perpetual virginity of Mary, male priesthood, salvation and a host of theological topics. Conversely the Catholic Church is routinely criticized for not changing with the times.