At some point in the history of the Christian Church, the Church chose the writings (gospels and epistles) of the Apostles and other disciples as the canonical inspired Scriptures. How were those Scriptures chosen? And what constitutes inspired Scriptures? How were they established?
Quite obviously the writings, which now constitutes the accepted Scriptures, were written by humans and not directly by God like He did when He wrote the 10 commandments (with Moses) on Mount Sinai using His own finger to write in stone. So what defines inspired writings in the vein of 2 Timothy 3:16?
All scripture is given by inspiration of God [meaning God breathed], and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
We know through the 1st to 3rd centuries AD there were many cults and schisms in the early Church over different heresies. There were many spurious writings claiming inspiration of God, including false gospels, some promoting pet heresies. Then in the modern period there have been much discussion about the preservation of the inspired writings.
In 1881 Westcott and Hort produced the first revised Greek NT manuscript, since the late 16th century, which they compiled largely from the Codex Sinaiticus, also known as “Aleph” (the Hebrew letter א), found by Tischendorf in 1859 at the Monastery of St Catherine on Mount Sinai, and, Codex Vaticanus, also known as “B”, which was found in the Vatican. It is not known when B arrived at the Vatican, but it was included in a catalog listing in 1475. Both of these manuscripts are dated to the 4th century.