C. S. Lewis, in Mere Christianity, gives a very helpful illustration. Imagine we are a fleet of ships sailing in formation to a particular destination. Now if the fleet is going to arrive safely without mishap, three things are necessary. First, the individual ships must be seaworthy. Their insides must be in good working order so they can keep afloat, steer well and have the motive power to make the journey. Second, they must be aware of the other boats so they don’t bump into one another and so cause harm to themselves and others. Third, they must have some idea about where they are heading – why they are afloat in the first place. It will be of no used if, after a good journey, they end up in Calcutta when they were supposed to get to New York