It is essential that we look at the Old Testament as a Christian book that was purposely written with the Christian in mind.
It is easy for us to think of the Old Testament as the book of Judaism, and that Christianity's roots are in Judaism. In fact, this idea is readily accepted in the "Christian world," but it is not true—not true in the least, except that there are some shared beliefs. If it were true, its modern corollary would be that Christianity's roots are also in paganism, because some of the concepts that pagans have are also shared with Christianity. That, incidentally, is what one large church has claimed in its writings about the holy days—that they actually derive from paganism.
The truth is that Judaism is a corruption of the religion God gave to Moses. It, too, was syncretic: part pagan, part truth, bound together by their own reasoning. In many places, Jesus corrected and railed against the Sadducees, the scribes, and the Pharisees. He said directly that they had rejected God's commandments in order to keep their own traditions. God's commandments are in the Old Testament; the Jews' traditions are not, and they are what the Jews lived by. Therefore, how can we say that Judaism came out of the Old Testament? God called the people out of Judaism to bring them into Christianity, just as today God is calling people out of a syncretic Christianity in order to bring them into true, biblical Christianity.
If Judaism really were God's religion, why did He not fix it from within? The period between the Testaments—between Malachi and Matthew—covered roughly 400 years in which a great deal took place. The record of Judaism during that time, particularly the history of the high priests, is much like that of the Papacy during the Middle Ages.
True Christianity's roots are in the truth of God—not only in the Old Testament, but also in the New. Judaism, though, rejects the New Testament, claiming the Old Testament as their book exclusively, and that perception is very strong to all. This world's Christianity claims the New Testament as its exclusive domain and virtually—and practically—ignores the Old Testament.