I don't understand in the epic of Gilgamesh a snake eating the plant to gain immortally why the serpent that is good symbol doing such a bad thing I mean he stole the plant from gelgamsh?
Mystic stories are for the very higher up spiritually advanced individuals to understand completely and interpret correctly. You and people who are reading this are very far away from this level.
A serpent eating a plant to gain immortality has nothing bad with it. "Stealing" is not literal.