"And he gave to Moses, when he had made an end of communing with him on mount Sinai, two tables of testimony, tables of stone, written with the finger of God" (Exodus 31:18 KJV).
Finger of God = God's spirit
An illustration might help us to understand what is being communicated here. A person can lose a finger, ear or toe without losing his/her identity, right? A body member is not to be equated with the whole person. Body parts are what could be called "accidents" (per accidens) or properties that we could do without while still maintaining our respective identities.
Now I'm not arguing that Jehovah God could ever lose one of his body members (he doesn't have any body "parts" to begin with), but we should make a distinction between a person's finger and the person him/herself. After all, the body of Christ (the ecclesia) is composed of many members (Rom 12:1-5); yet even if one of those members came down with (spiritual) gangrene and had to be lopped off, Christ's metaphorical body would continue to subsist because it is not absolutely identical with its respective parts (i.e., the whole is greater than the sum of its parts). The individual members just seem to constitute the whole body or provide some type of grounding for its existence.
Similarly, it's possible to distinguish between God's finger and his self. Why should we call the "finger of God," God tout court?