What is the lesson or moral lesson behind the story "The Myth of Demeter and Persepohne"?
I mean the lesson the story is teaching us as human, not the lesson to the characters in the story. Please help me.
It's a challenge to fully describe the myth of Demeter and Persephone as teaching a moral lesson. The myth's primary level of explanation or lesson might be more natural than all else in terms of explanation of the season change. On a more symbolic level, one can use the myth to teach the nature of creation and destruction being one in the same. The same regenerative forces that end up replenishing the earth and driving its bounty are also the same that bring coldness and a sense of desolation to the Earth. Demeter must live with the joy of being with her daughter, but is also bound to live with her absence. She is incapable of living a life that is totally present with happiness and elation. By the same token, she is relieved of living a life of total despair and misery. This might be the symbolic lesson to all readers, suggesting that consciousness is complex enough to bridge both the experiences that bring us happiness and the ones that cause us to hurt. Perhaps, there is a moral lesson here, after all.
From a less literary point of view, unlike my middle school teacher counterpart, you might be looking for the fact that through Greek mythology, the moral lesson taught to "young'uns" was that you should listen to parental figures or else bad things tend to happen. That is the dumbed-down version of the Greek myth of Demeter and Persephone.
Of course if you were looking for a more symbolic answer, akannan's pretty much sums it up.