There is so many interpretations this poem could have. I sense a longing for something followed by greed. This greed could be a woman or more than that. A dream where the living being sees himself as the king – who is the most powerful person in the kingdom. However, the dream could represent him wishing or longing for someone he loves. How at the end he is brought back to reality and that’s what I feel the message is. Do not higher your expectations so that they are escaping reality and be more down to earth – but hey that’s just my view on it.
Not long ago, in a charming dream, I saw myself -- a king with crown's treasure; I was in love with you, it seemed, And heart was beating with a pleasure. I sang my passion's song by your enchanting knees. Why, dreams, you didn't prolong my happiness forever? But gods deprived me not of whole their favor: I only lost the kingdom of my dreams.