There are probably several answers I could give such as: to become like Christ, to grow in holiness, to honor God, to show my absolute dependence upon Him for everything, to know more of God, to be a better husband, father, pastor, man, Christian, and the list goes on. However, my main reason is because the Bible is God's revelation of Himself to man. If we want to know God, we must know Him through the avenue that He has given us. We must read the Bible because in the Bible we see God!
From a pastoral standpoint, one of the things I've noticed most in the few churches I've served in is that most people do not even have the basic, overall view of the Bible. They know many things that have been told them (which we all do), but often times have never read the deeps trues that are found in the Scriptures (particularly the Old Testament). So with that being said, we need to capture a good overview of the Bible by reading through it each year (or more) so that we will better know God and be able to better worship Him in Spirit and truth. I plead with you my readers, read the Word of God this year!