Cyril of Alexandria
Catena Aurea · Lukasevangelium 11
But he, knowing their thoughts, said unto them, Every kingdom divided against itself is brought to desolation; and a house divided against a house falleth. If Satan also be divided against himself, how shall his kingdom stand? because ye say that I cast out devils through Beelzebub. And if I by Beelzebub cast out devils, by whom do your sons cast them out? therefore shall they be your judges. But if I with the finger of God cast out devils, no doubt the kingdom of God is come upon you.
Or the Holy Spirit is called the finger of God for this reason. The Son was said to be the hand and arm of the Father, (Ps. 98:1.) for the Father worketh all things by Him. As then the finger is not separate from the hand, but by nature a part of it; so the Holy Spirit is consubstantially united to the Son, and through Him the Son does all things.