That is a metaphoric language, in fact, the "hand of God" (cf. Isaiah 64:8) or "finger of God" (cf. Psalm 8:3) is a fixed metaphor for that, through which God creates universe, the entire created order of things, and therefore, the "hand" or "finger" of God cannot in principle be a created thing, unless we go to a negative infinity that this created "finger" through which God creates the world is also created by another created finger and so on. Therefore, when the Lord identifies this "finger of God" with the "Spirit of God" (Matthew 12:28), we see a clear evidence that the Spirit of God is not created, and what is not created, is God.
Now, we know, furthermore, that the Holy Spirit is a distinct Person, having the feature that only person can have, like willing (John 3:8; Acts 15:28-30), or cognizing (1 Cor. 2:10). And so, we have a clear theology of the Holy Spirit who is God, coming out from the God-Father (John 15:26) from whom He is distinct as the Sent is distinct from the Sender.
Moreover, the "finger" indicates that God-the-Father not only does not do anything without His Spirit, but also that He ontologically cannot do anything without His Spirit, like a surgeon not only does not, but cannot operate anyone without using his deft fingers. Which leads us to the necessary conclusion that the activity of the Father and the Spirit is one and the same divine activity conducted by distinct divine Persons.
Furthermore, the Lord says that the action of the Spirit and that of the Father, which action we have just proven to be identical, is conducted by Him, the Lord Jesus Christ, for He clearly says that “I expel demons”, and He does so out of His own authority, without invocation and prayer. Moreover, His disciples, who vicariously possess the ability of exorcising demons, do this by invoking His, Jesus’ name, that is to say, they invoke His, Jesus’ action (Matthew 12:27; Luke 10:17). This leads us to a further theological conclusion that also the Lord Jesus Christ co-acts with the Father and the Spirit in expelling demons, thus His own divine activity being also identical to the divine activity of the Father and the Spirit.
Now, given the principle that the activity is always an outcome of essence, the latter logically, if not temporarily, preceding the former, and given that entirety of the Father's activity is identical to the entirety of the Son’s and the Holy Spirit's activity, then we can freely conclude with the fathers formulating the Nicaean-Constantinopolian Creed (381 AD), that the Father and the Son and the Spirit have the same and identical divine essence.
Thus, this great theology is contained in the Lord's identification of the "finger of God" with the "Spirit of God".