I might recommend you read the Church’s Dogmatic Constitution on Divine Revelation, Dei Verbum. It’s not that long; can be read in one sitting.
vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_const_19651118_dei-verbum_en.html
Jesus taught orally. He never wrote a book, nor did He command anyone else to. He created a Church and trained Apostles to spread His message. Not everything Jesus taught was written down. (See John 21:25) Yet, He commanded the Apostles to go forth and teach “ALL” that He had taught them. (Matt. 28:20). The difference is Oral Tradition, also known as Sacred Tradition. ( 2 Thes. 2:15) SOME of what the Apostles passed down to their successors, the bishops, was written down. We call that the New Testament. But no book or message can stand on its own. It requires an authentic and authoritative interpreter. This is what we have in the Pope (successor to Peter) and the bishops in union with him. We call this group the Magisterium of the Church.
Practically speaking, the vast majority of earth’s population was illiterate for the majority of time Christianity has existed. Only in the last hundred years or so have a great number of people learned to read and write. Before that, it really wasn’t necessary. Most labor was manual labor.
The Bible, as we know it, didn’t exist till the 4th century, when the Church decided which books belonged in the Bible, and which did not. We have it on the authority of the Church what books belong in the Bible. The Church at that time went through over 300 books and letters, praying to the Holy Spirit to reveal to them which were Divinely inspired and which were not. They chose 27 from the 300+ documents, and that’s what we have in the New Testament today.
With regard to the Old Testament, there were two versions. Before Christ was born, there was a very large contingent of Jews in Alexandria, Egypt and surrounding areas (this was a big commerce port; Egypt was the bread basket of the Mediterranean). They wanted a version of the Jewish Scriptures, but they spoke Greek, not Hebrew. So, the Jews translated the Hebrew Scriptures into Greek. This was called the Septuagent version. Approximately 80% of the direct and indirect references in the New Testament to the Old Testament come from the Septuagent version, so we believe that’s the version most often used by Jesus and the Apostles, and that’s the version we use.
In the late first, early second century, the Jews decided to set the canon for their Scriptures. They were influenced by the fact that the early Christians were converting Jews using the Septuagent version, so they chose the Hebrew version. (This is a little oversimplified, but you should get the picture.) In the 1500’s when the Reformation came around, Martin Luther, on his own authority, decided to use the Jewish version. He didn’t like the Septuagent because it supported things he didn’t like, like Purgatory, etc. That’s why Protestants have 7 less books in their Old Testament than we do.
Also, there is no guarantee that any translation of the Bible is inerrant. All have some errors because there are some things that don’t translate well. For example, some things in the Greek don’t translate well into English. But the Bible was never meant to be a stand-alone instrument, or a be-all, end-all of the deposit of faith handed us by Christ. It is only a tool. Without Sacred Tradition and the Magisterium, you are assured to have errors in understanding.
