How important is the Old Testament to Christians? Many Christians entirely ignore it, or view it as simply a bunch of stories that tell us about the Jews. The amount of preaching that is done from the Pentateuch (first five books) or the rest of the Old Testament is amazingly small. Maybe it's because preachers don't think it's as relevant, maybe they think it's too filled with contraversy, maybe the New Testament just seems like better material. Whatever the reason, we need to objectively look at the importance of the Old Testament to believers today.
Whenever Jesus or the New Testament writers referred to Scriptures, it almost always meant the Old Testament. As such, the Old Testament was their Bible, and extremely important. Here are a couple of the things they said about it:
"You diligently study the Scriptures because you think that by them you possess eternal life. These are the Scriptures that testify about me" (Jesus, John 5:39)
"the Scripture cannot be broken" (Jesus, John 10:35)
"All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness" (Paul, 2 Timothy 3:16)
As I was reading my Old Testament Survey textbook (Old Testament Survey: The Message, Form, and Background of the Old Testament), it was mentioned that Jesus never disagreed with the Jewish leaders when it came to the authority and/or inspiration of the Old Testament. He battled them over many other topics, specifically relating to the interpretation of many Old Testament passages and ideas, but never disagreed that it was God's reliable word.
According to my OT Survey text, the two points that Jesus differed with the Jewish leaders on as it relates to interpretation of the Old Testament were:
1 - Legalism. Jesus had no patience for the substitution of rituals for what was in the heart. The Sermon on the Mount simply pounds that point home in the most amazing way.
2 - Jesus' identity. Jesus insisted that He was the fulfillment of the Old Testament prophecies regarding the Messiah. He insisted that He was the Messiah and indeed, God come in the flesh. Read the Gospels for the disagreement on this topic that just screams at you.
Here's a quote from the OT Survey that is just plain old beautiful:
"He (Jesus) looked upon the Scripture not as a catalogue of fixed principles regulating religious conduct, but as the inspired and authoritative record of God's activity in history, an activity which presses toward its climax in the kingdom which Jesus brought near." (587)
This should be our view of the Old Testament as well. This one sums it up.
"In study as in worship, humankind needs the entire revelation, the whole Bible. The Old Testament belongs not to the Jewish people alone but to all. It is the account of the ways in which God has worked; it is the summary of what he has demanded; it is the record of his preparation for Christ's coming; it is the best canvas on which to catch the picture of his dealings with the human family through the centuries. In short, it is the indispensable foundation on which the New Testament is built." (589)