And the Lord spake unto Adam, saying: Inasmuch as thy children are conceived in sin, even so when they begin to grow up, sin conceiveth in their hearts, and they taste the bitter, that they may know to prize the good.
And it is given unto them to know good from evil; wherefore they are agents unto themselves, and I have given unto you another law and commandment.
They taste the bitter, that they may know to prize the good
How do you know that you want to go to heaven? Because you have been told it is a place of peace and love. How do you know that you do not want to go to hell? Because you have been told it is a place of suffering and sorrow. But how do you know that you want peace and love, rather than suffering and sorrow? Because you have experience both, and therefore know which experience is pleasurable and which is painful. Even before you committed your first sin, you were educated on the differences between the two so thoroughly that you cannot mistake one for the other.
If you had never received that education, words like peace, love, pleasure, good, suffering, sorrow, pain, and evil would merely be words. Meaningless, and impossible to judge one against the other.
Wherefore they are agents unto themselves
So what is our purpose here on Earth? To gain knowledge, to learn the difference between good and evil, and to choose the better part. Because of our awareness we are able to choose a path. Not only that, but we can also turn to another path if we later change our choice. We are free to be our own agent, to steer ourselves to our own destination. We are not be some dumb entity that is puppeteered into its destiny, we choose it for ourselves.
And that is truly something worthy. For this, a God would die.