Once upon a time a boy was walking through the countryside when he saw, between some clouds, an angel singing a beautiful song. The angel soon disappeared.
The boy thought that it must be the doorway to heaven, and that it would be fun to see what was up there. So he started building a great big tower of wood, reaching up to the clouds. However, when the tower was very tall, it collapsed. He tried building it with adobe, with bricks, and then with steel, but his tower always collapsed.
Just when he was about to give up, the angel returned, this time surrounded by other angels. The angel sang again, and the boy listened closely. The message of the song was that one could only reach that heavenly place if you really wanted to, with all your heart.
No longer was the boy just curious, now he desired with all his might to go up and visit heaven with the angels. But he just couldn't manage it, and overcome by his sense of powerlessness and sorrow, he sat down and began to cry. He cried and cried and cried, so much so, that when the sun appeared from behind the clouds it created a magnificent rainbow. The rainbow led directly up to the doors of heaven.
The boy traveled up the rainbow, filled with joy, and knowing that only with sincere, heartfelt desire could one ever open the doors to heaven.