Behavioral Sin(s) vs. The Sin of Unbelief

There seems to be no real or good working definition for the distinction between our ‘sins’ of behavior/actions and the sin of unbelief. How can we really understand what Christ has done if we continue to misunderstand what sin really is? Most people oversimplify sin and make it apply in some general and generic way. Sin is commonly being taught as any transgression against God’s word and the law; and as much as that is absolutely true, there are a few details of distinction that should be point