The evil in the heart manifests itself in rebelliousness. Sin denies the relationship of the soul to its creator. It loses the fear of the Lord. This in turn exposes the soul to every attack of the enemy.
Sin makes the person blind, obstinate, and proud.
It teaches the self to depend on its own strength. It cautions against dealing with desires that go beyond its strength. It reminds the self of the many misfortunes and hurt it experienced, every time it trusted others. Sin is like a virus that keeps hiding itself. The effect is negligible and it influences every thought and desire.