As The Message was handed on from one generation to another,
human understanding of The Message continued to deepen

In time, the Apostles' successors decided, with the guidance of the Holy Spirit,
which books "made the cut" and would be considered as "Scripture"

This is how we got our Bible

The church in the fourth century  decided the Bible would have
46 Old/First Testament  books and 27 New/Second Testament books.
But this is not a simple issue - see link below

Thank you, Jesus, that in our day Christians have common Bibles.
May our love for the Scriptures promote Christian unity

How many books are in the Bible?  (see "Christian Canons")