Athanasius of Alexandria

And again, when He put a curb in the mouths of the demons that cried after Him from the tombs. For although what they said was true, and they lied not then, saying, 'Thou art the Son of God,' and 'the Holy One of Gods;' yet He would not that the truth should proceed from an unclean mouth, and especially from such as them, lest under pretence thereof they should mingle with it their own malicious devices, and sow these also while men slept. …

To The Bishops Of Egypt 1.3 ↗

Theophylact of Ohrid

But Christ silences him, so that we may know that demons must be stopped from speaking, even if they speak the truth. The demon throws and violently shakes the one it possesses, so that the onlookers, seeing from what a calamity the man is delivered, might believe on account of the miracle.

Commentary on Mark ↗

Bede

And Jesus rebuked him saying: Be silent, and come out of the man. For by the envy of the devil death entered into the world (Wisdom XII), therefore against the author of death itself, the medicine of salvation ought to work first: first the serpent's tongue, so that it may not spread poison further, be shut; then the woman, who was first seduced, be cured from the fever of carnal desire; thirdly, the man, who heard the words of his badly advising wife, be cleansed from the leprosy of his error, so that the order of restoration in the …

On the Gospel of Mark ↗