The Holy Spirit
The Catholic Church protected it and very carefully proclaimed, through the inspiration of the Holy Spirit, what needed to be in the NT. And yes, the Church authorized what books would be part of the canon.
It was a Catholic bishop about 700 years ago who decided that there should be Chapter and verse separation so that it would be easier to read.
The use of the word "Catholic" was introduced in the fourth century in order to differentiate between those groveling in heresy and those who stuck by the truth.
There is so much you guys do not know. As is everything that happened for 1500 years before Martin Luther was of no use to God.