Our Lord, here, is urging us to think, and to think in a Christian manner. That is the very essence of faith. Faith, if you like, can be defined like this: It is a man insisting upon thinking when everything seems determined to bludgeon and knock him down in an intellectual sense. The trouble with the person of little faith is that, instead of controlling his own thought, his thought is being controlled by something else, and, as we put it, he goes round and round in circles. That is the essence of worry. If you lie awake at night for hours I can tell you what you have been doing; you have been going round in circles. You just go over the same old miserable details about some person or some thing. That is not thought; that is the absence of thought, a failure to think. That means that something else is controlling your thought and governing it, and it leads to that wretched, unhappy state called worry.Martyn Lloyd-Jones, The Sermon on the Mount