The God-inspired books/writings of our current Bible are scripture. (2 Tim. 3:16-17, 2 Peter 1:20-21) Scripture does not evolve whereas traditions of men do.
The following is an excerpt from biblestudytools.com that addresses further your question:
"What is Canon?
Spurred by these dilemmas the church developed its list of canonical books. The following are guidelines for accepting a book into the New Testament:
1. Was the book written by a prophet of God?
2. Was the writer confirmed by acts of God?
3. Does the message tell the truth about God?
4. Did it come with the power of God?
5. Was it accepted by God’s people?
These are the
marks of canonicity. “Canon” is a Greek word meaning “rule” or “measuring stick.” These five questions are used to determine which books “measure up” to being labeled divinely inspired. They exhibit “the marks of canonicity.”
Turn to a Bible’s table of contents and you’ll see that each of the books was written by either a prophet or apostle (
Ephesians 2:20), or by someone with a direct relationship to one.
Miracles were the means by which God confirmed the authority of his spokesmen. In
Exodus 4, Moses was given miraculous powers to confirm his call. In
2 Corinthians 12:12, Paul teaches that the mark of an apostle is “signs, wonders and miracles.”
Truth cannot contradict itself, so agreement with the other books of Scripture was only logical. As was historical accuracy. If the facts of a book were inaccurate, it couldn’t have been from God.
The inner witness of the Spirit was equally important. A key question these early Christians asked was, When we read this, is there an inner sense from God that what is written is right and true?
Initial acceptance by people to whom the work was addressed was crucial. What was the original audience’s sense? Did they accept the book as an authoritative word from God? Daniel, who lived within a few years of Jeremiah, called Jeremiah’s book “Scripture” in
Daniel 9:2. Paul called the Gospel of Luke “Scripture” in
1 Timothy 5:18. Peter affirmed that Paul’s letters were “Scripture” in
2 Peter 3:16."