Gregory the Dialogist

If I laughed on them, they believed it not; and the light of my countenance fell not on the ground. If we understand this according to the words of the history, it must be imagined that the holy man had shewn himself such to those under him, that even in laughing he was able to be feared. …

Morals on the Book of Job, Book XX ↗

Thomas Aquinas

Second, he shows that he was moderate in his conversation, and not dissipated by joy, and so he says, "If I ever laughed at them," showing some signs of joy, "they did not believe," that I have surrendered myself to laughter. Likewise, he was not depressed by sorrow, and so he says, "and the light of my countenance was not cast down to the ground." For men depressed by mourning usually cast their eyes down to the ground.

Commentary on Job ↗