Anyone who has worked with clay will know that you can do nothing with it when it is hard. No matter how had you hit it, it will not change shape. The only way to change its shape is to pour water over it and carefully mould it into something beautiful.
The same thing happens with the human heart. Our hearts can become hard as a result of sin; either sin committed by us or against us. Normally we try to change ourselves (or other people) by beating them into shape. We try to ‘teach people lessons’, or shame them into changing.
The only way to change a human heart is to pour over it with the water of love and compassion. If we begin to accept other people (or ourselves) in spite of the faults that are so obvious, we find at the human heart is able to be gradually and gently be moulded into something beautiful.