Let us admit, he says, that I am iniquitous and impious; but I gain no profit from these remarks and know that you will mock me; therefore, I do not yield. “And what!” he says, “is it a mortal who blames me?” that is, no mortal can blame me. I am not fighting against a man. “When I think of it, I am dismayed and pains seize my flesh.” Notice how he always stands up, how he puts forward his sufferings, how he indicates the reason for the terrible words he is going to speak, because he does not talk in this manner by himself or from a fixed position but because his soul is dismayed and his thoughts are darkened.
43. i.e. Consider what I have done, and be astonished at the things that I undergo under this infliction of the rod. And he yet further rightly introduces the words; And lay your finger upon your mouth.
As if he had said in plain speech; 'Knowing the good things that I have done and seeing the ills that I am subjected to, your own selves keep even from offence in words, and in my strokes dread your own hurts.' Or indeed seeing that by our fingers we distinguish things severally, discretion is not unfitly represented by the fingers; and hence it is said by the Psalmist, Blessed be the Lord my God, Which teacheth my hands to war, and my fingers to fight [Ps. 144, 1]; i.e. by the 'hands' denoting practice, and by the 'fingers,' discretion. And so the finger is laid to the mouth, when the tongue is bridled by discretion, that by what it utters, it may not fall into the sin of foolishness. And therefore he says, Lay your finger upon your mouth; i.e. 'join the virtue of discretion to your speech, that in those things which ye say light against the hypocrite, ye may see to what persons they are proper to be said.'
[AD 407] John Chrysostom on Job 21:4-6