For the word of God [OT] is living and active and sharper than any two-edged sword, piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart. Hebrews 4:12 NASB
Do you need the Old Testament? Many people today, including some prominent preachers, say no. But they are wrong. You do need the Old Testament.
Why? The answer is pretty simple: you need the Old Testament to understand the New Testament correctly. The two testaments complement each other. Each one is incomplete without the other. For instance, it is very easy to make the God of the New Testament just a kindly grandfather who will let you get away with anything. On the other hand, it is very easy to make the Old Testament God a terrifying ogre who will strike you dead if you cross him. Neither view is correct. The perfectly pure God of the Old Testament loves you all the way to his own death on the cross, and the gracious God of the New Testament is the righteous Judge who will send you to hell. We need both testaments to get an adequate picture of God.
Here’s another example: the Cross is the answer, but what is the question? Why did Jesus die? If you only know the NT, you may well say that it is: how can my sins be forgiven so I can go to heaven? But that is wrong. The question the Cross is answering is the OT one: how can a holy God take up residence in a sinful person (OT). Does God want to forgive our sins? Of course. But that is the beginning of the story of redemption, not the end, as so many Christians tragically see it. He wants to forgive us so his Spirit can fill us and transform us into a holy temple for him to live in.
The Old Testament is a book of unanswered questions, but the New Testament is a book of pointless answers. Together, they are the full-orbed, exciting Word of God. The OT is a tough read, but if you will apply yourself to it, you will become a real Christian.
Called To Be Transformed 