Jesus said to them,

And beginning with Moses and with all the prophets, He explained to them carefully the things concerning Himself in all the Scriptures. Then, when the three of them sat down to eat, Jesus took some bread and after He had blessed it, He broke it and gave it to the two men.

It was then that their eyes were opened and they recognized Jesus Christ. Then Jesus disappeared from their sight, and the two said to one another,

Then He said to them, "These are the words which I spoke to you while I was still with you, that all things must be fulfilled which were written in the Law of Moses and the Prophets and the Psalms concerning Me." And He opened their understanding, that they might comprehend the Scriptures. Then He said to them, "Thus it is written, and thus it was necessary for the Christ to suffer and to rise from the dead the third day, and that repentance and remission of sins should be preached in His name to all nations, beginning at Jerusalem. And you are witnesses of these things." (Luke 24:44-48)

Thus Jesus was crucified and died and was raised from the dead three days later. After He had suffered in this way, He presented Himself alive, by many convincing proofs. He appeared to them over a period of forty days and spoke of the things concerning the kingdom of God. (See Acts 1:3)

If we consider the most important part of all of this, even when Jesus was born, the angel proclaimed,

Just as the angel revealed this about Jesus after His resurrection, Jesus Himself also said,

Also the apostle Peter wrote,

This blessed truth to which, through the grace of Jesus Christ, man's spirit has been called from his wanderings in darkness and the oppression of sin, is the news of God's tremendous love, which He promised beforehand in the Old Testament. This is the gospel that God promised in advance through His prophets in the Holy Scriptures. (See Romans 1:2).

Therefore the purpose of recording the Old Testament and that of recording the New Testament is to be found in the words Jesus spoke when He was living in the flesh, that is to say, before He was crucified:

At that time, whenever the Jews read the Old Testament, they did so in the hope of receiving eternal life, but Jesus Himself told them that the Scriptures, or the Old Testament, bore witness to the fact that He was the Christ. Also, the apostle John bore witness, saying that the Scriptures that make up the New Testament were recorded so that those who read them might believe that Jesus is the Son of God and the Christ, and that by believing in the name of Jesus, God's only begotten Son, they might receive eternal life.