Only through knowledge, he can decide whether he should speak the truth or tell the lie, whether he should comfort someone or cause grief. Knowledge makes him realize that good deeds lead to good results and bad deeds entrain bad results. Even then, trapped by inducements, he at times acts bad. This puts adverse effect on his mind and body. He is captivated by various diseases.
Pure knowledge breeds humanity.
In the absence of humanity, a man becomes a demon. He starts behaving against the Nature and the Nature punishes without avoidance. Man is helpless in front of this power. He can become happy, prosperous and great only by acting in accordance with Nature. In order to achieve good results from Nature, he has to perform well to become entitled to good results.