John Gill Commentary Matthew 28:4

"and for fear of him the watchers did quake, and became as dead men." — Matthew 28:4 (ASV)

And for fear of him the keepers did shake
Though they were soldiers, Roman soldiers and veterans, who had been used to terrible sights in the field of battle; were men of courage, and fearless of danger; and yet were seized with a panic, and every limb of them shook and trembled at the sight of the angel, for fear he had come as an executioner of divine vengeance upon them; who had been concerned in the crucifixion of Christ, had watched him as he hung upon the cross, and now his body in the sepulchre:

And even supposing no consciousness of guilt in them, or dread of punishment from him; yet such was the glory and majesty in which he appeared, of which they had never seen the like before, that it had this effect upon them:

and became as dead men :
they turned pale, as dead men, and had scarcely any life, or spirit, left in them.