They were the original authority as given them that position and charge by Christ himself, including Paul. Their view and expression of Christ is “everything” to the “truth” being presented and passed on as God intended. Each plays an interesting role, and also of note, those disciples who really are not heard from in bulk or accurately from the the time even post-ascension. and, their effect on not only the “players” of the day, but on all Christendom mark time throughout the ages for all believers. Ex. – Mark’s tutorials from Peter make the book a work for eternal purposes.
The early church fathers would have been the ones teaching and answering the questions of church members, new believers, and those seeking answers about Christianity. They were have been involved in real lives of real people with real struggles. Therefore, they would have turned to the Scriptures available to them for answers or to what teachings they had heard through word of mouth. Additionally they would have been asking for guidance from the Spirit of Christ. All of what they experienced, knew, and learned through this would be of great value to people as the fathers sought how to teach and answer their flock.