John Newton, in a letter to a friend, lays out why we are the way we are —
The holiness of a sinner consists chiefly of low thoughts of self, and high thoughts of the Saviour. These will always be in proportion. The lower we appear to ourselves, the more highly we shall esteem him. The more his glory strikes us, the more we shall sink in our own eyes. Could you find the man who has most of these properties, you would find the most holy man upon earth. And as we advance in these we shall in the same degree attain to everything else that properly belongs to holiness.
Why are we liable to anger, pride, and other evil tempers but because we think too highly of ourselves and suppose we are not treated as we ought to be? Why are we so apt to be captivated by the gewgaws of the world, but because we are so faintly impressed with a real sense of the excellence of Jesus? We say indeed that his loving-kindess is better than life, but if we really and fully thought so, hard things would be easy, and bitter sweet, and there would be no room for impatience or discontent in our hearts. But alas! all within us, and all around us is defective and polluted.