A bird had no interest in learning the song its master wanted to teach it while its cage was full of light. Its master covered the cage to darken it. He then whistled the same song over and over until the bird learned it by heart. When it could repeat it note for note, the owner uncovered the cage and the bird sang it beautifully. This is an illustration of the way God sometimes deals with us. He darkens the cage of our lives in order to teach us some divine song.
(source: Pulpit Helps)