Why is the Bible divided into Old Testament and New Testament?

Question

All the Bible I have seen (Catholic and Protestant) have the books in the Bible divided into two groups - Old Testament and New Testament. There is always a dedicated page just before the Book of Genesis with the title "The Old Testament" which indicates that the books that follow after this page falls under this category. There is also a dedicated page just before the Gospel of Matthew with the title "The New Testament" indicating that the books after this page are categorized as New Testament. I have also seen some Christians holding a small Bible having only the New Testament with Psalms and Proverbs as an addition. I wonder why do we have this division. I'm also perplexed by the use of the terms "Old" and "New". I need some historical and theological background to help me understand this division.

1. When did this division happen?
2. Why did they make this division?
3. Does this division bear any significant importance?
4. Can we simply divide the Bible as "Books written before Christ" and "Books written after Christ"?
5. Was the use of the terms 'Old' and 'New' accidental or intentional?
6. Is this division necessary?
7. Is there any Bible that doesn't have this division?

Answer 1

The New Covenant Foretold

The key to the division can be seen in Jeremiah, where God speaks of the old covenant and the new covenant. Israel had broken the old covenant, so God spoke of a new covenant.

31 “Behold, days are coming,” declares the Lord, “when I will make a new covenant with the house of Israel and with the house of Judah, 32 not like the covenant which I made with their fathers in the day I took them by the hand to bring them out of the land of Egypt, My covenant which they broke, although I was a husband to them,” declares the Lord.

33 “But this is the covenant which I will make with the house of Israel after those days,” declares the Lord, “I will put My law within them and on their heart I will write it; and I will be their God, and they shall be My people. 34 They will not teach again, each man his neighbor and each man his brother, saying, ‘Know the Lord,’ for they will all know Me, from the least of them to the greatest of them,” declares the Lord, “for I will forgive their iniquity, and their sin I will remember no more.” Jeremiah 31:31-35 NASB

The Breaking of the Old Covenant

The enumeration of covenants includes those with Noah, Abraham, Moses and David, among others. So, if we were being precise, we might say the "Old Testaments" (plural) and the "New Testament (singular). However, the primary covenant that governed all of Israel was probably the Mosaic covenant, which the people broke. The book of Hebrews affirms this:

6 But now He [Jesus] has obtained a more excellent ministry, by as much as He is also the mediator of a better covenant, which has been enacted on better promises. 7 For if that first covenant had been faultless, there would have been no occasion sought for a second. 8 For finding fault with them, He says,

“Behold, days are coming, says the Lord, When I will effect a new covenant With the house of Israel and with the house of Judah; 9 Not like the covenant which I made with their fathers On the day when I took them by the hand To lead them out of the land of Egypt; For they did not continue in My covenant, And I did not care for them, says the Lord. 10 “For this is the covenant that I will make with the house of Israel After those days, says the Lord: I will put My laws into their minds, And I will write them on their hearts. And I will be their God, And they shall be My people. 11 “And they shall not teach everyone his fellow citizen, And everyone his brother, saying, ‘Know the Lord,’ For all will know Me, From the least to the greatest of them. 12 “For I will be merciful to their iniquities, And I will remember their sins no more.”

13 When He said, “A new covenant,” He has made the first obsolete. But whatever is becoming obsolete and growing old is ready to disappear.

Jesus, the Mediator of the New Covenant

Jesus Christ is, thus, the mediator of the New Covenant, as Hebrews 12 affirms:

But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to myriads of angels, 23 to the general assembly and church of the firstborn who are enrolled in heaven, and to God, the Judge of all, and to the spirits of the righteous made perfect, 24 and to Jesus, the mediator of a new covenant, and to the sprinkled blood, which speaks better than the blood of Abel. Hebrews 12:22-24 NASB

The Inception of the New Covenant

This division is affirmed in several places. It was introduced by Jesus at the Last Supper.

23 For I received from the Lord that which I also delivered to you, that the Lord Jesus in the night in which He was betrayed took bread; 24 and when He had given thanks, He broke it and said, “This is My body, which is for you; do this in remembrance of Me.” 25 In the same way He took the cup also after supper, saying, “This cup is the new covenant in My blood; do this, as often as you drink it, in remembrance of Me.” 26 For as often as you eat this bread and drink the cup, you proclaim the Lord’s death until He comes. 1 Corinthians 11:23-26

Conclusion

So, everything does change with the coming of Jesus. The New Testament is the collection of all the books that being with the life of Jesus, the Mediator of the New Covenant.

Answer 2

1. The events, or historical division happened at the time of Christ's arrival. The New Testament books, of course, hadn't been written yet. The New Testament books were written after this event, and the canonization of Scripture happened later, by the fifth century A.D.
2. Because Christ is the fulfillment of the old Testament
3. Absolutely! The Old Testament dealt with the old covenant, which was the promise between God and His people based on obedience to Mosaic law. The New Testament is based on God's promise of eternal life, based not on man's ability to keep the law (we can't) but rather on the perfection of Christ and His substitutionary sacrifice. The division between the two marks two distinct covenants, the one replacing the other.
4. Sure, that's one way of looking at it. You might be interested in Why are the books of the Protestant Bible in the order that they are in? for a less simplistic view.
5. I'm sure that they are intentional. One is, after all, older than the other. (Implying that the other is the new one.)
6. Yes. Christ is the turning point. It is upon Him that all of Christianity is based.
7. (crickets chirping.) I can't answer that one. I'm not aware of any, but it's impossible to prove the non-existence of anything. But, remember that the Bible isn't one book, or even 2 - but rather 66 (or 73 if you're Catholic!). To not have a division is to misrepresent what these things are. It would be akin to going to a library and finding all the books shoved into one.

Answer 3

It is important to take note that there are assumptions in some of these answers. I would make a few points to stimulate thinking on this question.

1. The division, with a page, of the Tanakh/Hebrew Scriptures (OT) and the New Testament (Greek Scriptures) were not made under the inspiration of God (just as the chapters and verses are not, and perhaps some titles).

2. Jesus spoke of the New Covenant but never "the old". The term "old testament" was used once and "first testament" twice in the epistles. They didn't refer to the scriptures, but the covenant. In fact, the NT uses the term scripture or scriptures 53 times--this was how the apostles named the scriptures. Peter referred to Paul's extant writings as scripture while referring to the Tanakh (Gen to Mal) as scripture--he made no distinction. (True, when Moses put the first writings in the ark, it was referred to as the ark of the covenant or the ark of the testimony, but this was only the 10 Commandments or the 10 Commandments and the Book of Exodus).

3. All the apostles and Jesus considered the "scriptures" to be the Law and the Prophets or Moses and the Prophets, etc. This has been abandoned--but it is the biblical way of referring to the scriptures--the actual name. The word Tanakh is the acronym of Torah, Nevi'im, Ketuvim: the Law, Prophets, Writings. This is the shorthand way to say it. This would be closest to the way Jesus would refer to the scriptures. (Along this line, speculation alert: he might call the NT in its entirety, the Gospel)

4. I couldn't disagree more strongly against this opinion/doctrine, but some/many hold that everything that occurred in the Gospels was old covenant and must be disregarded as our rule for living under the new. In this case, all the Gospels should come after Malachi and the separation should be with perhaps Acts.

5. The dividing page is entirely man-made in that no books were in existence in the first century; all scriptures were in rolls and they would be kept together without distinction. Many books would require more than one scroll. Obviously, since the writings of the NT did not come in the order of the Bible today, we don't know if they were combined in unexpected ways: perhaps a scroll with some letters of Paul and Peter and a Gospel. We just don't know. There were pocket gospels available in the second century.

6. Heresy entered the church early. Marcion, who hated YHVH (the demiurge) with a dark passion is credited with popularizing the term Old Testament because these scriptures were evil and the God in them was evil--distinct from the God of the NT. Early, the church became virulently anti-semitic (John was discriminated against, as is written in his epistle). The desire to put a division between non-messianic Jews and Gentile Christianity as it grew, was immense. Christian writers after the first and second century exude hatred toward the Jewish people. This lasted for millennia.

7. If time and covenant were to be the division standard: There were hundreds of years between Genesis and Exodus--we don't have a division there (400 between Malachi and John the Baptist). If distinct covenants were the standard, then we would have more divisions: especially the Abrahamic, Mosaic, Davidic.

8. Regarding the question: "Why are the books of the New Testament attributed to people who probably didn't write and likely couldn't read?" I don't understand if the question is sincere. Of course, the scriptures were written by people who could write. Writing was in existence before Moses. Moses could write. The Hebrew's/Israeli's culture was based on their religious beliefs--directed by a God who gave His word to His people in written form--the only systematic, historically accurate history written by a "religion". The emphasis on the entire people mastering the scriptures was immense: this includes reading the scriptures, the writing of which is an integrated discipline. Because some of the apostles were fishermen or carpenters, in no way implies illiteracy.