Why doesn't trying to cover up sin solve the problem?
Covering up sin fails because the real source is old Adam, the sinful nature that keeps producing sin like a still keeps producing alcohol. Wallpapering over the output does not remove the root. The problem is solved only by dealing with old Adam, not by concealment or human effort.
Les explains that in the bootlegging days, authorities could outlaw alcohol, but they could not stop people from getting it. The only way to deal with the problem was to find where it was made and get rid of the stills. In the same way, old Adam is like a still that keeps putting out sin. No matter how someone tries to cover it up or wallpaper over it, it will not work until old Adam is dealt with. Les also stresses that no one can approach God on the merit of what they have done, and Abraham believed God, and his believing caused God to call him a righteous man.