The Bible consists of sixty-six books, thirty-nine of which compose the Old Testament. Firstly, the Bible states that God changes not, and He is the same yesterday, today and forever. If God therefore does not change, the God of the Old Testament is the God of the New Testament. To learn of how God deals with his people (Israel, also of which the Gentiles, which are other nations, are grafted to the tree), the history of the Patriarchs and expectations of the Old Testament it is good to study the Old Testament. We learn later in the New Testament that we are not justified by the laws of Moses but Faith in Jesus Christ. In the Old Testament, we are told that certain foods we must stay away from, but we learn in the Book of Acts that all creatures are clean and can be eaten, it is what comes out of a man’s mouth that defiles Him (as stated by Jesus).
Jesus Christ is the Word made manifest. The Word was present before the creation of the world, and the Word is above God’s name, all of which are stated in the Bible. The Old Testament scriptures prophesy of the coming of Jesus Christ in the flesh. Jesus states in the Gospels, He is the chief cornerstone that the builders rejected (prophesy of Jesus’ crucifixion), and Rachel weeps for her children, which are not (prophesy of the children two years old and under executed by Herod when Jesus was born). Also the Word states, “there is one crying in the wilderness, make way for the Lord!”, a prophesy of John the Baptist. If Jesus is the Word made flesh, we should study the Word as much as we can to understand Jesus and the prophecies. Actually the Old Testament books contain prophesies in the future that have not occurred yet but describe the second coming of Christ and the apocalypse. So the Old Testament is still relevant today, but the New Testament is probably the most important to understand for new Christians, as it sums up the most important aspect of salvation, Faith in Jesus Christ.