Luther reflects on the difference between what we want and what we need:

A cup of water, if a man have no better, is good to quench the thirst. A morsel of bread stills the hunger, and he that needs it seeks it earnestly. Christ is the best, surest, and only physic against the most fearful enemy of mankind, the devil; but men believe it not with their hearts. If they want a physician, living a hundred miles off, who, they think, can drive away temporal death, oh, how diligently is he sent for – no money or cost is spared! But the small and little heap only stick fast to the true physician, and by his art learn that which the holy Simeon well knew by reason of which he joyfully sang: “Lord, now lettest thou thy servant depart in peace, for mine eyes have seen thy salvation!” Whence came his great joy? Because that with spiritual and corporal eyes he say the Saviour of the world, the true physician against sin and death. `Tis a great pain to behold how desirous a thirsty man is of drink, or a hungry man of foot, though a cup of water or a morsel of bread can still hunger and thirst no longer than two or three hours, while no man, or very few, desires or longs after the most precious of all physicians, though he lovingly calls us to come unto him, saying, “He that is athirst, let him come to me and drink,” (John 7).