Not the commenter but it's just a interesting premise. It's an old King who's experienced every earthly pleasure in existence (food, wine, servants, women, etc.) who is looking back on his life and writing a letter to his son. He is basically despairing that all of these things were in vain and that they don't mean anything now that he is old, etc. It doesn't really have a clean payoff or moral either, the premise is basically "life sucks, pleasure is fleeting, and then you die".