Ba'al Shem Tov, Bereshit 94/בעל שם טוב על התורה·בראשית צ״ד

1When you speak, you should feel fear, for the World of Speech is the World of Fear. But when you speak about matters of love and fear, you should first feel fear, and then fiery enthusiasm.Tzava’as HaRivash, p. 10b