Opening his mouth. It is a Hebraism, to signify he began to speak. (Witham)
This is a common expression in Scripture, to signify something important is about to be spoken. Thus it is used in various other places, as "Job opening his mouth cursed his day, and said "Daniel, chap. x. et alibi. (Jansenius)
And why is it added, says St. Chrysostom "and opening his mouth "without doubt that we might know, that not only when he spoke, but even when silent, he gave instruction: sometimes, therefore, he opened his mouth; at other times he spoke by his very actions. (Hom. xv.)
