St. Ambrose of Milan ca. 338-397
Now what ought we to learn before everything else, but to be silent, that we may be able to speak? Lest my voice should condemn me, before that of another acquit me; for it is written: By your words you shall be condemned.
Mat. 12:37 What need is there, then, that you should hasten to undergo the danger of condemnation by speaking, when you can be more safe by keeping silent? How many have I seen to fall into sin by speaking, but scarcely one by keeping silent; and so it is more difficult to know how to keep silent than how to speak. I know that most persons speak because they do not know how to keep silent. It is seldom that any one is silent even when speaking profits him nothing. He is wise, then, who knows how to keep silent. Lastly, the Wisdom of God said: The Lord has given to me the tongue of learning, that I should know when it is good to speak.
Justly, then, is he wise who has received of the Lord to know when he ought to speak. Wherefore the Scripture says well: A wise man will keep silence until there is opportunity.
Sirach 20:7
Therefore the saints of the Lord loved to keep silence, because they knew that a man’s voice is often the utterance of sin, and a man’s speech is the beginning of human error. Lastly, the Saint of the Lord said: I said, I will take heed to my ways, that I offend not in my tongue.
For he knew and had read that it was a mark of the divine protection for a man to be hid from the scourge of his own tongue, Job 5:21 and the witness of his own conscience. We are chastised by the silent reproaches of our thoughts, and by the judgment of conscience. We are chastised also by the lash of our own voice, when we say things whereby our soul is mortally injured, and our mind is sorely wounded. But who is there that has his heart clean from the impurities of sin, and does not offend in his tongue? And so, as he saw there was no one who could keep his mouth free from evil speaking, he laid upon himself the law of innocency by a rule of silence, with a view to avoiding by silence that fault which he could with difficulty escape in speaking. (On the Duty of Clergy Bk. 1: Chap. 2.5-6)