To Know Christ

For if ye believed Moses, you would believe me; for he wrote of me. But if you believe not his writings, how shall you believe my words?

John 5:46 - 47

Consider this: Jesus said that we must believe Moses' words (ie, the Law or the Old Testament) and if we believe not Moses' words, we cannot believe Christ's words.  To understand and know and believe Christ fully is to understand and know and believe the words written down in the Old Testament.  This should not surprise us for Christ Himself spoke to the disciples on the Road to Emmaus and "interpreted to them in all the scriptures the things concerning himself, beginning from Moses and from all the prophets" (Luke 24:27).

Putting it another way, your theology will be weak and anemic at best if it neglects Scripture in the Old Testament.  But more seriously, your theology may miss the mark entirely if you do not believe the writings of Moses and the prophets—for "how shall you believe [Christ's] words?"