The reality or essence of faith is discovery of God. When a person becomes aware of God’s existence and apprehends divine realities, that is true faith.
Such a discovery is no simple matter. God is the Creator and Lord of all things, He is the One who awards punishment and no one can escape His grasp. The discovery of such a God has a profound effect upon the whole life of the individual. His thinking is revolutionized to the extent that God becomes the centre of all his emotions.
As a consequence, the believer surrenders him being to God. God becomes the centre of all his attention. Now he becomes a person whose life and death are for God alone.
The result of this faith is that a person’s behaviour throughout his life becomes dyed in the hue of God. When he speaks, he is conscious that God is hearing him and when he walks, he takes care that his way of walking is not of one who struts arrogantly. When he deals with people, he is fearful lest he do anything unjust such as would incur God’s punishment.
As a result of this faith, a person’s entire life becomes oriented towards the Hereafter. In all matters, his eyes are on the Hereafter. In this world, instead of temporary gains, he makes the gains of the Hereafter the centre of his attention. When there are two sides to any matter – the worldly side and the otherworldly side, he ignores the consideration of this world and chooses what would be of value in the life Hereafter.
For him this faith becomes a source of limitless trust in God. At all times and in all events he puts his trust in God. Faith in essence is to have recognized the Lord when this recognition or discovery becomes a part and parcel of a person’s heart and mind. Then his whole personality is transformed. He becomes a new human being.
Source: A Simple Introduction to Islam