The phrases ξὺν νόῳ (with understanding) and ξυνῷ (to the common) are very similar.  Heraclitus is most likely playing on this words.  No matter how much learning a person has, he will not have understanding if he turns aside to his own private world (B40, B129).

Many see the reference to 'the divine one' as 'the divine law.'  I do not think this is what Heraclitus is saying.  The Greek ἑνὸς τοῦ θείου should be read as 'the divine One,' meaning 'the one divine being.'