Luke 10:18

Now He says that He saw it, as being Judge, for He knew the sufferings of the spirits. Or He says, as lightning, because by nature Satan shone as lightning, but became darkness through his affections, since what God made good he changed in himself to evil.

(Hom. Quod Deus non est auctor mali.) He is called Satan, because he is an enemy to God, (for this the Hebrew word signifies,) but he is called the Devil, because he assists us in doing evil, and is an accuser. His nature is incorporeal, his abode in the air. (adv. Eunom. l. 3.) For the heavenly Powers are not naturally holy, but according to the analogy of divine love they receive their measure of sanctification. And as iron placed in the fire does not cease to be iron, though by the violent application of the flame, both in effect and appearance, it passes into fire; so also the Powers on high, from their participation in that which is naturally holy, have a holiness implanted in them. For Satan had not fallen, if by nature he had been unsusceptible of evil.

Or else, I saw Satan as lightning fall from heaven, that is, from the highest power to the lowest impotence. For before the coming of our Saviour, he had subdued the world to him, and was worshipped by all men. But when the only-begotten Word of God came down from heaven, he fell as lightning, seeing that he is trodden under foot by those who worship Christ. As it follows, And, behold, I give unto you power to tread upon serpents, &c.

(23. Mor. c. 4.) Now our Lord, in a remarkable manner, in order to put down high thoughts in the hearts of His disciples, Himself related the account of the fall which the teacher of pride suffered; that they might learn by the example of the author of pride, what they would have to dread from the sin of pride. Hence it follows, I beheld Satan as lightning fall from heaven.

He says not, 'I see now,' but referring to past time, I saw, when he fell. But by the words as lightning, He signifies either a fall headlong from the high places to the lowest, or that now cast down, he transforms himself into an angel of light. (2 Cor. 11:14.)