Cyril of Alexandria — as excerpted in the Catena Aurea on Luke 11:17-20

“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.”