The world has no peace because it is in a sinful state. The same holds true for an individual. For someone in the Lord, the conscience could be sharpened to the point that any sin committed against God becomes so distasteful as to be unbearable. The great saints would rather die than sin against God. This loss of internal peace is proof that sin and peace cannot coexist. Then, at the opposite end, there are those whose conscience has been dulled to the point that they can easily sweep their sins under the carpet. Even though they look away from their sins, the lack of peace remains in their heart.