"And he said to them, 'Is a lamp brought in to be put under a bushel, or under a bed, and not on a stand? For there is nothing hid, except to be made manifest; nor is anything secret, except to come to light'" (Mark 4:21-22 RSV).
I've added verse 22 to complete the thought. At this point Jesus has just begun his teaching ministry, starting with the parable of the sower. His disciples do not understand it, and when the crowds have dispersed they ask him to explain the parable. After he does so—and adds that there are many more parables still to come—he explains why these teachings are important. The "lamp" is the new spiritual Truth that he embodies. Its purpose isn't just to transform his life or the lives of his immediate followers; it's to transform the world. A personal Truth could be kept secret—hidden under a bushel basket or under a bed, its presence known to just a few. His spiritual message, on the other hand, must go on a lampstand, to be seen by all—whether or not they understand. It's true for us as well, I think. Each of us is that lamp—an aspect of spiritual Truth that we are here to share freely by being the light in expression. Such a light has no concern about where it shines or to whom. It simply shines and draws to itself those who are able to see it and appreciate it.