I thought I'd copy something written in a previous thread...
Looking back right after Christ ascended into heaven and the Holy Spirit came upon on the disciples, and the Christian Church was born. Many Jews and Gentiles were converting to Christianity. In their church services, they were using the Jewish scriptures. This didn't sit well with the Jews, so they held a council. They met to go through their scriptures and determine which ones were authentically inspired by God.
In Palestine, the scriptures were recorded in Hebrew. In the Alexandrian territory, they were recorded in Greek, the common language of the time -- that was also the dominantly used version. The Jews in their pursuit to find true, authentic books, they only looked at the scriptures recorded in Hebrew. Any books that were not in the Hebrew were thrown out (First and Second Maccabees, Wisdom, etc.).
Throughout the early Church, these books continued to be used from the Greek. When they started to write their own letters and gospels, they were referring to this Greek text -- the Greek version of what we call the Old Testament. In 393 and again in 397, the Catholic bishops gathered and held a council to figure out which writings were truly inspired by the Holy Spirit -- especially what we now call the New Testament. Up until that time, they didn't have a cannon that included the NT. As they went through the readings, they got rid of the ones that were not inspired by the Holy Spirit and kept the ones that were. So every Bible today, NT cannon, was given to us by the Catholic bishops. Anyone who puts their faith in the Bible, especially the NT, puts their faith in the ability of the Holy Spirit to direct the Catholic bishops to lead us to the truth -- in this case, on the cannon of scripture.
That cannon was held to be the true cannon of scripture all the way up to the Protestant reformation in the 1500s -- so we had over 1000 years where we operated on that cannon of scripture. At the time of the reformation, Martin Luther broke away and began to change dogmatic and doctrinal teachings, and also wanted to change the cannon of scripture. At this time, the Catholic Church definitively stated that this was the true authentic cannon of scripture given to us by God. However, because some of the books didn't support Martin Luther's theology, he wanted to change the cannon.