Seeing the Bible as One Book
A key to understanding the Bible, Old and New Testament, is seeing it as one progressive story about Jesus and Him crucified. The New Testament writers as they were being directed by Holy Spirit saw Jesus Christ as fulfillment of the Old Testament promises, prophecies, and types (typology). (see references from books of John & Hebrews below)
Heb 1:1-2 Long ago God spoke many times and in many ways to our ancestors through the prophets. And now in these final days, he has spoken to us through his Son. God promised everything to the Son as an inheritance, and through the Son he created the universe (nlt)
Jhn 1:1-3 In the beginning the Word already existed. The Word was with God, and the Word was God. He existed in the beginning with God. God created everything through him, and nothing was created except through him. [The Word was Christ]
Jhn 1:10-14 He [Christ] came into the very world he created, but the world didn’t recognize him.  He came to his own people, and even they rejected him. But to all who believed him and accepted him, he gave the right to become children of God. They are reborn—not with a physical birth resulting from human passion or plan, but a birth that comes from God.  So the Word became human[fn] and made his home among us. He was full of unfailing love and faithfulness.[fn] And we have seen his glory, the glory of the Father’s one and only Son. (nlt)
The Old Testament is the promise, and the New Testament is the fulfilment. Christ is promised in the Old, and revealed in the New. So we should not think that the two Testaments are unrelated, or that the Old Testament represents God’s Plan for Israel, which failed, and was replaced by the New Testament, God’s Plan for the church.
The Bible teaches that God is all knowing and all powerful. He sees the ending from the beginning.
1 John 3:20 ESV For whenever our heart condemns us, God is greater than our heart, and he knows everything.
Isa 46:9-10 Remember the former things of old: for I am God, and there is none else; I am God, and there is none like me, Declaring the end from the beginning, and from ancient times the things that are not yet done, saying, My counsel shall stand, and I will do all my pleasure:
The whole Bible is a self-interpreting book, and we can understand neither Testament without the other. The Biblical (story) revelation is gradual and cumulative, and events and people in the Old Testament foreshadow those New Testament, with New Testament revelation having a greater significance. In fact this was seen by the church fathers over fifteen hundred years ago. For example St Augustine made the statement, ‘The New Testament lies hidden in the Old, and the Old becomes manifest in the New.’
Paul states that he only wanted to know and preach Jesus!
1Co 2:1-2 When I first came to you, dear brothers and sisters,[fn] I didn’t use lofty words and impressive wisdom to tell you God’s secret plan.[fn] For I decided that while I was with you I would forget everything except Jesus Christ, the one who was crucified. (nlt)
Paul in a few verses later tells them why the mystery of the crucifixion was concealed.
Co 2:7-8 No, the wisdom we speak of is the mystery of God[fn]—his plan that was previously hidden, even though he made it for our ultimate glory before the world began. But the rulers of this world have not understood it; if they had, they would not have crucified our glorious Lord.
When Jesus was crucified the veil was ripped, not only to allow access into the “Holy of Holies”, but also ripped the veil for understanding the Old Testament in light of the New, ONE story of Jesus fulfilling the Old Testament promises, prophecies, and typology!
There is continuity between the people of God in the Old Testament and the church, the people of God in the New Testament. God is unchanging and His message through New Testament writers was the same as the message of the Old Testament. Both John and the writer of Hebrews is making the same point above.
Paul is clearly making that point in 1 Cor 10:1-11 where he says that the Old Testament contained examples (“types”) for us the church) today.
1Co 10:1-5 I don’t want you to forget, dear brothers and sisters,[fn] about our ancestors in the wilderness long ago. All of them were guided by a cloud that moved ahead of them, and all of them walked through the sea on dry ground. In the cloud and in the sea, all of them were baptized as followers of Moses. All of them ate the same spiritual food, and all of them drank the same spiritual water. For they drank from the spiritual rock that traveled with them, and that rock was Christ.  Yet God was not pleased with most of them, and their bodies were scattered in the wilderness.
Paul summarizes the “wilderness experience” found in the “Exodus Story” of the Torah, first five books of the Old Testament as a “type”/example. Then in 1 Cor 10:6-11 Paul applies them to us (the church) the anti-type.
 These things happened as a warning to us, so that we would not crave evil things as they did,  or worship idols as some of them did. As the Scriptures say, “The people celebrated with feasting and drinking, and they indulged in pagan revelry.”[fn] And we must not engage in sexual immorality as some of them did, causing 23,000 of them to die in one day. Nor should we put Christ[fn] to the test, as some of them did and then died from snakebites. And don’t grumble as some of them did, and then were destroyed by the angel of death. These things happened to them as examples for us. They were written down to warn us who live at the end of the age.
Then in 1Co 10:12 Paul warns us (the church)!
“If you think you are standing strong, be careful not to fall.”
This concept (typology) is important because the New Testament writers very often read the Old Testament in a typological way. They see “types” many places and in turn use “anti-types” in their New Testament account as Paul in 1 Cor 10 above.
It makes perfect sense to apply God’s words to his people in the Old Testament (Israel) to his people in the New Testament (the church), and to expect common experiences in the lives of both. This is expressed both in terms of similarity and contrast, as in 1 Corinthians 10:1-11, Hebrews 3:7-4:11, Hebrews 10:26-31, and Hebrews 12:18-29. The two Testaments have the same theological content in different forms, and in different stages of revelation. Both are about God, and both are about Christ. ‘For no matter how many promises God has made, they are “Yes” in Christ’ (2 Corinthians 1:20).
Jesus is ‘the bread of life,’ more wonderful than the manna God provided in the wilderness. People who ate that manna still faced death. Those who eat the bread of life have eternal life, and Jesus’ flesh is that bread—which he will give for the life of the world (John 6:30-51).
God is unchanging and is author of both the Old and New testament. It is one complete message about Christ! Yet the New Testament like the book of Hebrews shows that the Old Testament revelation and God’s revelation in his Son are one message showing the Son, Christ, as superior to (completes/fulfills) Old Testament revelation.
Mat 5:17-18 “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.  For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished.
A person must be “born again” of the Spirit of God for veil of the Old Testament to be understood in light of the Gospel of Christ.
2Co 3:15-16 Yes, even today when they read Moses’ writings, their hearts are covered with that veil, and they do not understand. But whenever someone turns to the Lord, the veil is taken away.