כי שם הי אקרא הבו גדל לאלקינו
The Tur writes that he heard from his father (the Rosh) that when one hears a blessing one says, “Baruch Hu u’vrach Shmo” (ברוך הוא וברוך שמו). This is what Moshe Rabenu taught in the about pasuk. So is the halacha in Shulchan Aruch (O.Ch. 124).
The Baruch SheAmar says there was a possible reason to refrain from saying these words. In prior generations, some were careful to say ברוך הוא ברוך שמו since they said intended to the false moshiach Shabatai Tzvi (who has the same Gematria of 814). However, The Baruch SheAmar says the Tur made sure that the phrase had the letter Vav ברוך שמווברוך הוא equals 820 and no longer equals the same Gematria.