It is an every day experience that when you do not know a thing, you look for some one who knows it and you repose faith in his word and follow him. If you get ill and you can not treat and cure your self, you look for the doctor and accept and follow his instruction without question. Why? Because he proper qualified to give medicine dvice, possess experience, and treated and cured the number of patients. You therefore stick to his advice, do what ever he asks you to do and avoid what ever he forbids. Similarly, in matters of law you believe in whatever your legal adviser says and acts accordingly .In educational matters you have faith in your teacher or instructor and you accept his instructions as true. When you want to go some place and do not happen to know the way to it, you ask somebody who knows it, and follow the way he points out. In short, the reasonable course that you adopt in the whole of your life about matters which you do not or cannot know is that you approach one who knows them, accept his advice, and at accordingly. As your own knowledge of that matter or problem is inadequate, you carefully search for one who knows that and then silently accept his word. You take every pain to select the proper person. But after selecting the right man, you accept his advise and unquestioningly. This kind of belief is called 'belief in the unknown '. For here you have relied upon one who knows, in matters you don't know this exactly is Iman-bil-ghaib. Thus believing or having faith in what was previously unknowing to you is called 'faith in the unknown'.( Iman-bil-ghaib).
Iman-bil-ghaib therefore, signifies that you achieve the knowledge of what was not known to you from one who knows. You do not know God and his real attributes. You are not aware that His angles are directing the machinery of the whole universe according to His orders, and that day surround on all sites. You have not the proper knowledge of the way of life through which you can seek the pleasure of your Creator. And you are in the dark about the life that is to come. The Prophets, who had direct contact with the Divine Being and had being endowed with the correct knowledge, gives the knowledge of all this matters to you. And they are the persons whose sincerity, integrity trustworthiness, godliness and the absolute purity of whose lives stand as irrevocable witnesses to the truth of their claim to knowledge. And above all , the very wisdom and force of their message makes you admit that the speak the truth and their preaching deserve to be believed and followed. This conviction of yours is Iman-bil-ghaib. Such truth - discerning and truth - acknowledging attitude (i.e. Iman-bil-ghaib ) is essential for obedience to God and for acting in accordance with His pleasure, for you have no other medium than God's Messenger for the achievement of true knowledge and, without accurate and true knowledge you cannot proceed rightly on the path of Islam.