“When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own but will speak whatever he hears, and he will declare to you the things that are to come” (John 16:13).
When I use the word Church, I am referring to the Christian Community worldwide. I am not talking about an organization, institution, or building.
Scripture
The Bible is authoritative because the Church says it is. The Church created the Bible, the Bible didn’t create the Church. That is why the Bible is not the only source of the Christian faith. Tradition is alao authoritative.
Tradition
Paul tells his followers to live “according to the tradition that they received from us” (2 Thess. 3:6). That they are to “stand firm and hold fast to the traditions that you were taught by us, either by word of mouth or by our letter” (2 Thess. 2:15). So oral tradition was a real thing.
Worship
But so is the manner of worship. The Latin phrase, lex orandi, lex credendi, catches this. It means that the law of what is prayed is the law of what is believed. Our relationship with God influences our beliefs.
The Didache is the oldest church manual, which tells us how the church practiced their faith. The Book of Common Prayer has had a profound effect on the Anglican Church throughout the world. All this is part of Tradition.
The Church
So the authority in Christianity lies in the Church, not in a book, a pope, or a patriarch. It is our collective voice that sets the standard for our sources of faith and practice.
We can and often do make mistakes, but the Spirit will ultimately “guide” us “into all the truth.” We must be humble and teachable and open to not only Scripture and Tradition, but also reason and personal experience. And reason includes listening to the evidence from science, history, and modern scholarship.