John Chrysostom

"And when forty years were expired, there appeared to him in the wilderness of mount Sinai an angel of the Lord in a flame of fire in a bush." Do you mark that it is not hindered by lapse of time? For when he was an exile, when a stranger, when he had now passed much time in a foreign land, so as to have two sons, when he no longer expected to return, then does the Angel appear to him. The Son of God he calls an Angel, as also he calls Him man. Appears in the desert, not in a temple. …

Homily on Acts 16 ↗

Theophylact of Ohrid

But his flight did not disrupt God's plans either, because it is said: "when forty years were fulfilled, the Angel of the Lord appeared to him in the wilderness of Mount Sinai" — He appeared when Moses was in flight, when he did not even hope to return, since he already had two sons. But notice: Stephen now calls the Son of God both an Angel and a man. And the Angel appears to Moses not in a temple, but in the wilderness, and not simply in the wilderness, but in a bush — in the flame of a burning thornbush.

Commentary on Acts ↗

Oecumenius

Now he calls the Son of God an angel, just as elsewhere he calls him a man. For he is the angel of great counsel. (Isa. 9:6 LXX) Therefore shortly afterwards he shows him speaking to the blessed Moses: "I am the God of your fathers, the God of Abraham, and of Isaac, and of Jacob." He is revealed in a flame of fire in a bush. For in the form of fire and on Mount Sinai God appears while giving the law. What then does the passage mean? The sacred text likens the divine nature to fire because it overpowers wood and grass, that is, man. …

Commentary on Acts ↗