The truth is that the human being has a basic difference with all other creatures of the universe and that is having free choice and will.
Why did God create the human being free and give decision-making power so that he or she can do whatever he or she wants to do?
The reason is that if he or she were not free, there would be no transformation and this great possibility is a guarantee of spiritual and ethical transformation. For instance, if a person is forced at sword point to help the deprived and to do good deeds for society, of course, this would be considered to be good deeds, but no ethical or human transformation would take place for the person who was forced to do this.
Thus the first condition for a spiritual and ethical transformation is that free will or freedom of choice must be present and available so that the human being can take this way by himself or herself and not through force. It must be like a natural force of the world of nature and if God has given this great gift to human beings it is because of this very elevated goal. But this blessing is just like a flower along which grows thorns and it is the misuse by individuals of this freedom and pollution with oppression and corruption.
Of course, as far as God is concerned, there would be nothing to prevent Him from punishing a human being with the worst kind of punishments if he were to commit oppression so that he would never consider doing it again, his hand be paralyzed, his eye lose sight, or his tongue not be able to Speak.
It is true that if this was the case, no one would misuse freedom and would never commit sins but this piety and devoutness has a coercive side and would in no way be considered to be an honor for the human being but rather it would be because of the fear of immediate punishment.
Thus, at any rate, the human being must be free and must be tested in various ways by the Creator, be free from immediate trial, other than in exceptional cases, to Show the value of his or her self.
Ref: Fifty Lessons of Principles of Belief for Youths; Ayt. Makarem Shirazi; Translated by: Bahador Shirazian; Published by: Ahlul Bayt World Assembly