In a real conversation, different people have different vocabularies, different speech patterns and rhythms. Do the characters in your dialogue sound like one person talking out of both sides of his mouth? In many of Andrew Marvell’s dialogues, whether the character is called Body, Soul, or anything else, it still sounds like Marvell speaking. This might not matter in personifications of the Body and Soul, but in a more concrete poem with human characters, there really should be some differentiation between, especially with male and female characters. The author once read a review of Atlas Shrugged by Ayn Rand that said of her characters that all of the men were basically the same personality, and the main woman character was just the same man in a skirt. To really create a believable poetic conversation, you must truly have different characters, otherwise when you write the conversation, even if the two voices disagree, it sounds like the old, “I agree, Doctor, but on the other hand, don’t you think…“ sort of conversation.