As human beings, we are very visually oriented. The things we can see and feel and interact with are the things which affect us most. Consequently, we can tend to put a great focus on sins which are visible, while sometimes ignoring sins which may be of equal or even greater magnitude but cannot be seen, because they are in the heart. Perhaps the greatest of all these hidden sins is that of unbelief - not only is it not doing what God commands us to do, it is calling the God of Truth a liar, implying that we know better than He does! We must be especially aware of this sin for it does not only affect unbelievers. Christians can lose assurance, joy and power through unbelief. However, no true believer can lose his salvation and we know from the Bible that God will forgive and restore those who are prone to doubt and uncertainty.