John Chrysostom

"And fear came upon every soul": of those that believed. For they did not despise the Apostles, like common men, nor did they fix their regard on that which was visible merely. Verily, their thoughts were kindled into a glow. And as Peter had before spoken much, and declared the promises, and the things to come, well might they be beside themselves with fear. …

Homily on Acts 7 ↗

Theophylact of Ohrid

"There was... fear on every soul," because they did not disregard what was happening as something accidental. Since Peter was filled with abundant grace and was revealing the promises and the future, it was very natural that they were seized with fear, especially since he confirmed his words with the miracles and signs he performed. As with Christ—first signs, then teaching, then miracles—so also now.

Commentary on Acts ↗

Oecumenius

For they did not despise those who happened to be there, but because Peter was a great figure, flowing from above, and showing the things to come by his promises, they were rightly afraid. For the works bore witness to the word. Just as before with Christ there were first signs, then teaching, then miracles, so now also.

Commentary on Acts ↗