Albert Barnes Commentary Luke 10:18

"And he said unto them, I beheld Satan fallen as lightning from heaven." — Luke 10:18 (ASV)

I beheld Satan, and so on. Satan here evidently denotes the prince of the devils who had been cast out by the seventy disciples, for the discourse concerned their power over evil spirits. Lightning is an image of rapidity or quickness. I saw Satan fall quickly or rapidly—as quick as lightning. The phrase "from heaven" refers to the lightning, and does not mean that he saw Satan fall from heaven, but that he fell as quick as lightning from heaven or from the clouds. The whole expression then may mean:

"I saw at your command devils immediately depart, as quick as the flash of lightning. I gave you this power—I saw it put forth—and I give now also, in addition to this, the power to tread on serpents, and so on."

"Satan as lightning" (Revelation 12:8–9).