A famished Fox saw some clusters of ripe black grapes hanging from a trellised vine. She resorted to all her tricks to get at them, but wearied herself in vain, for she could not reach them. At last she turned away, hiding her disappointment and saying: “The Grapes are sour, and not ripe as I thought.”
Taken metaphorically, this interpretation can be presented to polytheists as follows. Beware of blaming the Gods when you are unable to fulfil your presumptuous attempts of reaching their height, knowing them fully, keeping company with them, or attributing divine titles to yourself, because you can’t and you shouldn’t.