We must have standards and authorities in all the affairs of life. If we do not, then we have much confusion. Every nation has a government which exercises authority over it. The headmaster and teachers exercise authority in the school.
Parents exercise authority in the home.
In Christianity we see much division and confusion. The result is hundreds of churches with many different teachings. Before this confusion can be cleared, we must all agree on an authority in Christianity. The Bible is the authority in Christianity because it is the inspired Word of God. Peter is talking about the men who wrote the Bible.