The contents page of the Bible shows that the Scriptures are divided into two parts: the Old and New Testaments. The word "testament" used in this context means a covenant, agreement, promise or pledge between two parties.
The teaching of the Bible is based upon covenants of promise that God made with faithful men in times past. The Bible teaches that:
"Jesus Christ [came]. . .
to confirm the promises made to the fathers, and that the Gentiles might glorify God for His mercy. . ." (Romans 15:8-9). And, again: "By which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world through lust" (2 Peter 1:4). The Bible, in fact, is a book of promise.
The Lord Jesus Christ is described as the Mediator of the "new covenant" (Hebrews 9:15). The events surrounding the ministry of the Lord Jesus Christ provide a natural means of division in Scripture, between those writings dealing with the Old Testament and those of the New Testament.
It must be remembered, however, that this division of the Scriptures into Old and New Testaments is man-made. The whole Bible is the revelation of God, and is one complete, indivisible book.
The Bible itself confirms this. In 1 Timothy 5:18 the Apostle Paul cites two passages, both of which he calls "Scripture." The first passage, "You shall not muzzle an ox while it treads the grain," is cited from Deuteronomy 25:4 in the Old Testament. The second passage, "The laborer is worthy of his wages," however, is a direct quote from Luke 10:7 (see also Matthew 10:10). Thus 1 Timothy 5:18 demonstrates that Paul considered passages from both the Old Testament and what became the New Testament to be inspired Scripture.
Some claim that the Old Testament became outdated when Christ appeared nearly 2000 years ago, but that is not so. The New Testament constantly refers the reader back to the Old. Christ, in preaching, told his listeners to "search the Scriptures" (John 5:39), by which he meant the Old Testament (as the New Testament was not yet written).
Christ appealed to these same Scriptures to expound the things concerning himself: "And beginning at Moses and all the Prophets, He expounded to them [the disciples] in all the Scriptures the things concerning Himself" (Luke 24:27). The Bible will never be properly understood if the Old Testament is neglected. The Gospel itself is based upon an Old Testament promise, as we read in Galatians 3:8: "[God] preached the gospel to Abraham beforehand, saying, 'In you all the nations shall be blessed.'"
To illustrate this, consider the following promises or covenants made by God in the Old Testament:
1. In the garden of Eden following the sin of Adam and Eve:
"And I will put enmity between you and the woman, and between your seed and her Seed; He shall bruise your head, and you shall bruise His heel." Genesis 3:15
2. Promises to Abraham, Isaac and Jacob--the "fathers of old:"
"I will make you a great nation; I will bless you and make your name great; and you shall be a blessing. I will bless those who bless you, and I will curse him who curses you; and in you all families of the earth shall be blessed." Genesis 12:2-3
3. Promise to David:
"When your days are fulfilled and you rest with your fathers, I will set up your seed after you, who will come from your body, and I will establish his kingdom. He shall build a house for My name, and I will establish the throne of his kingdom forever." 2 Samuel 7:12-13
4. Promises of the Kingdom to the prophets:
"For unto us a Child is born, unto us a Son is given; and the government will be upon His shoulder. And His name will be called Wonderful, Counselor, Mighty God, Everlasting Father, Prince of Peace. Of the increase of His government and peace there will be no end, upon the throne of David and over His kingdom, to order it and establish it with judgment and justice from that time forward, even forever." Isaiah 9:6-7
The angel Gabriel's testimony in the New Testament alludes to all these Old Testament promises:
"And behold, you will conceive in your womb and bring forth a Son, [the seed of the woman] and shall call His name Jesus. He will be great, and will be called the Son of the Highest; and the Lord God will give Him the throne of His father David [promise to David]. And He will reign over the house of Jacob forever [the seed promised to Abraham], and of His kingdom there will be no end [the promise to the prophets]." Luke 1:31-33
Another example of how God's promises span the Testaments is found in Paul's letter to the Galatians:
"And the Scripture, foreseeing that God would justify the nations by faith, preached the gospel to Abraham beforehand, saying, 'In you all the nations shall be blessed.' So then those who are of faith are blessed with believing Abraham . . . if you are Christ's, then you are Abraham's seed, and heirs according to the promise." Galatians 3:8-9, 29
God's promises are not yet complete. This is made evident through the prophecy of Jeremiah:
"Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah . . . I will put My law in their minds, and write it on their hearts; and I will be their God, and they shall be My people . . . they all shall know Me, from the least of them to the greatest of them, says the Lord." Jeremiah 31:31-34