How was the Bible decided?
The cannon of the Bible was solidified at the Council of XXXX, but the Bishops there mostly just made official what the Church already knew and used. Some texts were soundly rejected (such as the "Gospels" of Thomas and Peter, which are often called the "forgotten" or "lost" texts). The books of the Apocrypha were deemed important but not inspired, which is why in the 16th century Protestants rejected those books from being printed with the Bible. In response, the Council of Trent (1546) decided they were inspired to found the Catholic church. In general, Christians believe the cannon is closed (cannot be added to) and that it contains all that is required for life, belief, and salvation.