Please Mr. Postman by The Beatles is about a person eagerly waiting for a letter from their significant other. The song captures the anxiety and anticipation of waiting for communication from a loved one, emphasizing the importance of the mailman in delivering this crucial message. Key themes include love, longing, and impatience. Poignant moments in the song include the repeated pleas to the postman to check for the letter, highlighting the emotional weight and personal significance of the awaited correspondence.