In order to understand the being and nature of the Satan one should know that there are two faculties that God has granted to the human beings; both these qualities are contrary to each other. And it is so because God would like to test the human beings as to how they would fare for his communion. One of these two faculties is that of virtue and it pulls the man towards religious deeds. The other faculty is the one that invites him to evil deeds. The faculty that draws the man towards virtue is called the Angel and the other one that calls him to evil is known as the Satan. In other words it can be said that there are two faculties working in conjunction with man. One calls him towards virtuous deeds and the other calls him towards evil deeds. Anyone who does not like the words the Angel and the Satan may try to understand this situation by thinking of two faculties – Virtuous and evil. This, nobody can deny.
God has never willed anything that can be called bad. Whatever He does is all good and nothing but good.
Behold! if there had been nothing like evil in the world, the virtue also would not have existed. Virtue is known by its comparison with evil just as evil is known by its comparison with virtue. For instance, if somebody has the opportunity to commit adultery and at the same time has the power to perpetrate this deed, yet he shuns it, we would call this act of his (to avoid adultery in these circumstances) an act of virtue. If somebody has the opportunity to steal or to do injustice and he is in a position to do these things yet he keeps away from these things he does an act of virtue.
Let it be understood well that to have the opportunity of committing sin and yet avoiding it is virtue and that is what deserves good reward.