Imam Sadiq (a.s) said: “Man's pillar is the intellect. Wisdom, understanding and knowledge are all rooted in the intellect, and are perfected by it. The intellect is man's guide, vision and key to his affairs. When man's intellect is certified by divine light, he will become understanding, wise, (a mental), guardian (of the Quran), and knowledgeable. Then he will know where he is, what he is and why he is there. He will know his friends and his enemies. Then he will know the way to live, to arrive and depart. He will sincerely confess to the unity of God and obey Him. Then he can make up for what is lost, and be in control of the future. He will know his position, why he is where he is, and where he has come from, and to where he is going. All these are certified by the intellect.”