The Old Testament was written by God's inspired prophets, patriarchs, psalmists, judges, and kings. It was faithfully copied and preserved by Jewish scribes. Modern Protestant Bibles have the same content as the Hebrew Bible.
The New Testament was written by Christian apostles.
None of them were Catholics, because there was no Roman Catholic Church at the time. This was over two centuries before Constantine's "conversion".
The early Church did not have the New Testament as we know it. Rather, individuals and local congregations had portions of it. They would have one or more of the Gospels, some of the letters which Apostles had written, and perhaps the Book of Acts or the Book of Revelation.
Why weren't all of these books collected in one place? Look at what the books themselves say. Individual apostles wrote them for specific audiences. For example, the Gospel of Luke and the Book of Acts were written for Theophilus. (Luke 1:3; Acts 1:1) Most of the Epistles were written to specific churches or to specific individuals. (Romans 1:7; 1 Corinthians 1:2; 2 Corinthians 1:1; Galatians 1:2; Ephesians 1:1; Philippians 1:1; Colossians 1:2; 1 Thessalonians 1:1; 2 Thessalonians 1:1; 1 Timothy 1:2; 2 Timothy 1:2; Titus 1:4; Philemon 1:1; 3 John 1:1)
The early Christians expected that Jesus would return for His Church at any moment. As a result, they didn't see the need for long-term planning for future generations. Furthermore, Christians were persecuted by the Romans. When your life is in constant danger, it is difficult to collect writings which are scattered all over the Roman Empire. So it took time to collect all of these writings, decide which ones were authoritative Scripture, and make complete sets of them.
By the time of Origen (185-254 A.D.), there was general agreement about most of the New Testament. However, there was disagreement as to whether the following six epistles should be part of the New Testament canon: Hebrews, James, 2 Peter, 2 John, 3 John, and Jude. This was sixty years before Constantine's "conversion" and the formation of the Roman Catholic Church in 314 A.D. By 367 A.D., all of the books of the New Testament were acknowledged as being authoritative Scripture. [Note 17]
The canon of the New Testament was not formed by the decision of any Church council. Rather, the Council of Carthage (397 A.D.) listed as canonical "only those books that were generally regarded by the consensus of use as properly a canon". [Note 18] In other words, it didn't create the canon. Rather, it formally identified the canon that already existed.
So the Catholic Church did not give us the Bible. However, it did help confirm the authenticity of six New Testament epistles. Also, Catholic monks faithfully preserved the Bible by copying it.The Catholic Church changed the Bible. In 1548, at the Council of Trent, it added the Apocrypha to the Bible. The apocryphal books contain passages which are used to justify some Catholic doctrines, such as praying for the dead. The Apocrypha are discussed in Appendix B.
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