Shakyamuni Buddha taught how difficult and wonderful it is to be born a human in the Miscellaneous Agama Sutra. It's the "Parable of the Blind Turtle and the Log."
One day Buddha asked his disciple Annan a question.
"At the bottom of a vast ocean there is a blind turtle. Once every 100 years, the turtle pokes its head out of the water. Floating on the surface of the ocean is a log. In the middle of the log is a hole. The log drifts wherever the wind takes it, east and west, north and south. Annan, what are the chances that when that blind turtle comes up, its head would go into the hole in the log?"
Annan said "World-Honoured One, such a thing could hardly happen!"
“You’d think not,” Buddha replied. “But neither can you rule out the possibility that it might happen once in many trillions of years or more. To be born human is still more difficult and wonderful than this story suggests.”
This parable shows us just how rare and precious it is to be born human. But how do we actually feel about it? Far from feeling joyful, in hard times we may even resent our births. “Why did I have to be born? If only I had never been born, I wouldn’t have to suffer like this,” we lament. Why can't we appreciate our lives? It is because people are in the dark about the purpose of life. Why were we born as humans? Why are we alive? Why must we keep on living no matter how painful life is? When it comes to the very purpose of life, we are lost.
Only when the true purpose of life is achieved can we truly rejoice: “This is what I was born for. How glad I am that I was born human!” When the ultimate mission of life is finally realized, for the first time, the profound JOY OF LIFE arises in our heart. Then what is the important purpose that we can fulfill only as human beings?
Our chance to be liberated from the six realms
Buddha taught that our lives have a boundless history. We have been continuously suffering in realms of delusion over the course of many lifetimes and countless aeons— a mind-bogglingly long time.
It is taught that there are six realms of delusion.
The realm of heavenly beings
The realm of humans
The realm of asuras
The realm of animals
The realm of hungry ghosts
The realm of hell
All beings travel endlessly back and forth among the various realms of illusion, in constant suffering. This is known as ‘transmigration in the six realms’ or ‘the endless wheel of suffering’. Buddha said that to be liberated from these realms of delusion and live in eternal happiness is the very purpose of listening to Buddhism. In order to attain this goal, we have to be born human.
Human form is difficult to obtain;
Now I have already obtained it.
Buddhism is difficult to hear;
Now I have already heard it.
If I do not achieve salvation in this lifetime,
When will I ever do so?
To be born human is a rare blessing— a blessing that is ours. Hearing Buddhism is a rare blessing—a blessing that is ours.
I must be saved in this life by all means. If not, in what life will I be saved? This is my one chance in eternity.
Shakyamuni was teaching us here that the reason why we were born as human beings is to listen to Buddhism (Amida Buddha's Primal Vow), put a stop to the endless cycle of transmigration, and attain absolute happiness.
When the purpose of life is achieved, for the first time, it becomes very clear why a single human life outweighs the earth. You will know just how much you owe your parents and ancestors for having been born into this world.
The six worlds
The realm of hell:
The realm of extreme agony.
The realm of hungry ghosts:
In this realm, when beings try to eat or drink, all the food and drink turns into fire, so they are unable to consume anything. Because of this, these beings are extremely thin and continually suffer from hunger and thirst.
The realm of animals:
The world of dogs, cats, and other animals. In this realm, the strong prey on the weak, so beings live in constant fear.
The realm of asuras:
A realm of conflict in which beings suffer because of ceaseless fighting.
The realm of humans:
A realm where beings experience a mixture of pain and pleasure. This is the realm in which we live.
The realm of heavenly beings:
The world of ample pleasure. The suffering that beings experience here is lighter than that of other realms. However, this is also a realm of delusion. Their lives are limited, and their pleasure does not last.