Know that belief is different from the knowledge of God and His oneness, or the other attributes of His perfection, whether affirmative or negative, and from the knowledge of the angels, the messengers, the revealed books, and the Day of Resurrection. Many people have all of this knowledge without being believers. Satan himself knows all these things as well as you and I, and he is an unbeliever. Someone who acquires the knowledge of something by means of rational proof or conformity to religion must in addition submit to the object of that knowledge; he must bring about a state of surrender and humility, of acceptance and assent, in his heart in order to become a believer. The perfection of faith lies in tranquillity (itmi’nan), for once the light of faith has become strong, it will produce tranquillity in the heart.
All of this is quite different from knowledge. It is possible that your intellect should perceive something by means of a rational proof, but until your heart has submitted that knowledge is of no use. For example, intellect enables you to understand that a dead person cannot harm you in any way, and indeed that all the dead in the world do not have as much capacity for sensation or motion as even a fly, for all faculties, corporeal and mental, have left them. But since you do not accept this in your heart, because your heart has not submitted to what your intellect tells you, you could not endure the darkness of a night spent in the company of a corpse. Were your heart to submit to your intellect and to accept its instruction, such a prospect would present no difficulty. If you applied yourself to the task, in the end you would have no fear of the dead. It is thus apparent that submission, which is a quality pertaining to the heart, is different from knowledge, a quality pertaining to the intellect.
It is entirely possible that someone should be able, by means of rational proof, to prove the existence of the Almighty Creator and His oneness, the Day of Resurrection, and all the other true doctrines. But proving the veracity of those doctrines does not constitute belief, and the one proving them does not count as a believer; he may be an unbeliever, a hypocrite, or a mushrik. Today your eye is closed and does not have the vision of the unseen; the corporeal eye is incapable of seeing. When innermost secrets are revealed and the true sovereignty of Allah manifests itself, when the natural realm is destroyed and reality becomes utterly clear, then you will become aware that you were not believers in God. The activity of the intellect has no connection to belief. Until la ilaha ilia 'llah is inscribed by the pen of the intellect on the pure tablet of the heart, one is not a believer in God’s oneness.
And once that pure and sacred word has entered the heart, sovereignty over it belongs to God Almighty Himself; you will not permit anyone to exert any influence on what has now become God's realm. You will not expect splendor or rank, seek fame or dignity, from anyone. The heart will then be fully purified of hypocrisy and pretense. So if you see any hypocrisy in your heart, know that your heart has not submitted to your intellect, that belief has not illumined your heart, that you have granted divinity to one other than God and regarded one other than Him as the source of effects in this world. You belong, therefore, to the category of the hypocrites, the mushrikitt or the unbelievers.