“Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh’s heart was hardened, and he hearkened not unto them; as the LORD had said” (Exodus 8:19).
If ever we wonder about the meaning of a certain Bible expression, it is best to search for another verse that uses it. Using this method, we can restrict possible definitions, eliminate senses, and identify the most likely explanation. “The finger of God” appears four times in the King James Bible; its first occurrence is today’s Scripture. Let us look at those remaining instances.
Exodus 31:18 says the following: “And he gave unto Moses, when he had made an end of communing with him upon mount Sinai, two tables of testimony, tables of stone, written with the finger of God.” Reading Deuteronomy 9:10: “And the LORD delivered unto me two tables of stone written with the finger of God; and on them was written according to all the words, which the LORD spake with you in the mount out of the midst of the fire in the day of the assembly.”
Finally, the Lord Jesus Christ said in Luke 11:20: “But if I with the finger of God cast out devils, no doubt the kingdom of God is come upon you.” This verse is especially helpful in identifying “the finger of God,” for its parallel verse, Matthew 12:28, says: “But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.” Notice how “the finger of God” and “the Spirit of God” are used interchangeably—they are synonyms.
Therefore, the Bible phrase “the finger of God” should be taken to mean the Person of God the Holy Spirit. By the Holy Ghost, the Godhead judged wicked Egypt for enslaving His people, the nation Israel. By the Holy Ghost, the Godhead issued their divine and living words to Israel. Finally, by the Holy Ghost, the Godhead purged Israel of Satanic possession and influence. While it is commonly assumed the Holy Spirit is not found in the “Old Testament,” we can clearly see this is an erroneous supposition. source