In chapter 15, God outlines many restrictions and guidelines when dealing with people who had various infirmities. These guidelines weren’t arbitrary, they were for the express purpose of preserving his chosen people. God knows what is best for us and his word gives us that information. Wisdom comes when we follow what God says and apply his guidelines to our life.
Atonement is reconciliation or restoration or the relationship between God and man. In chapter 16, God describes the events of the day of atonement that the children of Israel would have to observe every year in perpetuity. When Christ died on the cross, we received everlasting atonement!