The Old Testament makes up nearly three-fourths of the Bible. It’s a huge chunk of it. While Jesus’s time on earth is recorded in the New Testament, the Old Testament contains prophecies foretelling of the coming of Jesus. This is just one of the reasons why the Old Testament is important.
Some Christians believe that the Old Testament is irrelevant to today’s world. They think that all you have to worry about are the teachings in the New Testament. However, that is not necessarily the case for Jesus said:
This doesn’t mean that we still burn sacrifices to God or anything, for Jesus was the ultimate sacrifice that made it so that we wouldn’t have to do that anymore to get forgiveness of our sins. In short, while most Christians no longer practice all aspects of Mosaic law like “an eye for an eye, a tooth for a tooth,” that doesn’t mean that the teachings in the Old Testament aren’t still important for us to study and apply to our daily lives.
The following link is an excellent resource I found explaining why the Old Testament is important. I encourage you to check it out if you have a moment.