Jerome

However, because of his fear, the guards were terrified and became like dead men. But the angel, responding, said to the women: Do not be afraid. For I know that you seek Jesus, who was crucified: He is not here, for he has risen as he said. The guards, terrified by fear, lie stupefied like dead men, and yet the angel comforts not them, but the women. Do not be afraid. Let them, he says, fear: let fear continue in those in whom unbelief persists. …

Commentary on Matthew ↗

Thomas Aquinas

And for fear of him, the guards were struck with terror. Here the effect of the apparition is set forth, because fear arose in their hearts; and rightly so, because they guarded him out of a bad conscience, and wickedness is always fearful, Wis. 17:10. And they became as dead men, they who wanted to hold Christ in death as far as it was in their power; Isa. 33:3: at the voice of the angel the peoples fled.

Commentary on Matthew ↗

Peter Chrysologus

For they kept watch over Him with a purpose of cruelty, not with the solicitude of affection. And no man can stand who is forsaken by his own conscience, or troubled with a sense of guilt. Hence the Angel confounds the wicked, and comforts the good.

Catena Aurea by Aquinas ↗