Many of the laws in the Old Testament were given only for the people of that time, and they no longer apply to us as Christians now that Christ has come. The New Testament says, "Now that faith (in Christ) has come, we are no longer under the supervision of the law" (Galatians 3:25).
For example, many of those laws dealt with the sacrificial system God established to take away their sins. These detailed regulations taught them that God is holy, and that sin is serious in His eyes - so serious it can only be cleansed by the shedding of blood. But those sacrifices are no longer needed, because Jesus Christ shed His blood as the final and complete sacrifice for our sins. The Bible says, "He has appeared once for all ... to do away with sin by the sacrifice of himself" (Hebrews 9:26).
I suspect, however, that even if you explained this to your friend he'd only come up with another question - and then another. In other words, his real problem is his will; he simply doesn't want God to interfere with his way of living. Ask God to help you confront him with this truth, clearly and yet in love.
Then pray for your friend. He needs Christ - and only God can convict him of this and convince him of the truth of the Gospel. But in the meantime, ask God to help you be a living demonstration to him of Christ's love and peace.