The Old Testament is important to us, if for no other reason than to have insight into what God intended for us, and what displeases Him most. It also gives us valuable knowledge about His love for us, and how our ancestors erred, so that we can learn from their mistakes.
Most of the rules of the Old Testament were about social living, cleanliness and moral structure. Remember that God was taking a people out of an ancient primitive culture, and renewing His contact with men. He was isolating them from the dangerous and idolatrous world at that stage, and giving them repetitive lessons to bring them into awareness of a higher way of life. The law was somewhat imperfect in that respect, because the nature of man is such that we tried to "get by" with just following the rules, rather than incorporating the goodness of their wisdom into our hearts.
Over and over, the chosen people, those whom God had set aside for Himself and remained in the presence of, made mistakes. They sought the physical pleasures of life, the false "assurance" of fortune telling, and almost as "insurance - just in case", they created other gods to worship. They were dealing with human emotions, human wisdom (which is foolishness), and the prompting of the fallen angels working for our enemy, attempting to keep mankind in the dark and away from God's true power.
When enough of them turned their hearts from God and began living as the other cultures around them did, in idolatry, God would allow suffering to come on the people. If they did not listen to His prophets who warned them, then they would be carried away captive by another nation, such as the Philistines, Babylon, etc.
When they finally turned their hearts back to God and repented, He miraculously rescued them, restoring their land and wealth, their health and their joy.
Now I know that most of you are thinking to yourselves, "I wouldn't have been so stupid! I never would have disobeyed God if it had been me, back then."
Beloved, I can promise you that you and I are no different from those people in this respect. We can take a lesson from our own behavior so far. How many times have you done something that you KNEW was wrong, but willfully did it anyway? Even if you have somehow managed to live a nearly perfect life and the worst thing you ever did was take a stick of chewing gum from a friend or classmate without permission...you have done the same things and longed for the same things.
When you get angry at someone, or talk about someone... When you tell others something that makes a person look bad, but makes you feel better to pretend that you are above that mistake... When you know someone else is in need, and you don't help... When you allow your body to rule your mind and heart, with food or sex, cigarettes or alcohol...
We have all sinned and fallen short of the Glory of God, but there is GREAT news!!! God says that right now, there is no condemnation for those who walk after the spirit and not after the flesh. That means that if you have accepted Jesus' sacrifice for your sins, and are living for God's will not your own to be done, then your sins are washed away and forgotten. As far as the east is from the west He has removed our sins from us. This is the GREAT Gift of the New Testament! It's the new covenant that we have through Jesus.