Matthew 5:17-19 (TLB)
"Don't misunderstand why I have come--it isn't to cancel the laws of Moses and the warnings of the prophets. No, I came to fulfill them, and to make them all come true . With all the earnestness I have I say: Every law in the Book will continue until its purpose is achieved. And so if anyone breaks the least commandment, and teaches others to, he shall be the least in the Kingdom of Heaven. But those who teach God's laws and obey them shall be great in the Kingdom of Heaven."
There is a tendency among Christians to place "the Laws of Moses", or what we call the Old Testament, on the back burner so to speak. The common belief is that these books are not relevant to us and our time because we have a New Covenant through Christ our Lord and Savior. It's very true that we do have this New Covenant but Jesus Himself here states that this New Covenant does not supercede nor does it cancel what He here refers to as "the Book". The moral, spiritual and physical laws and ordinances laid down in our Old Testament are just as relevant and necessary for us today as they were for the Israelites when God first carved them on two stone tablets.
The words of warning that came by way of His prophets then are just as valuable to us now as they were to Israel then and perhaps even more so considering the world we live in. The books of the Old Testament, as Jesus as told us, will stand until their purpose has been completed. And, as He has also said, those of us who teach them must not only teach but we must obey them as well. Practice what you preach in this instance is not just a saying but should be our constant and heartily desired goal.