Charles Ellicott Commentary Matthew 12:28

"But if I by the Spirit of God cast out demons, then is the kingdom of God come upon you." — Matthew 12:28 (ASV)

By the Spirit of God — In Luke 11:20, we have an equivalent phrase: the finger of God. Likewise, in Old Testament language, the fullness of the prophet’s inspiration was expressed in the words, the hand of the Lord was strong upon me (Ezekiel 3:14).

The second hymn in the Ordination Service reproduces this symbolism in the words addressed to the Holy Spirit:
In faithful hearts you write your law,
The finger of God’s hand;
and it obviously connects with the older language describing the Ten Commandments as written on the two tablets of stone with the finger of God (Exodus 31:18).

Then the kingdom of God has come upon you — The word describes a coming that is sudden, unexpected, and sooner than people anticipated.

The argument can be summarized as follows: The work was admittedly superhuman, coming either from the power of Satan or the power of God. The former hypothesis was excluded by the reasoning of Matthew 12:25-27; therefore, the latter was the only explanation.

But if this is so—if Jesus gave proof that He was filled with the power of the Spirit to heal and save—then He was what He claimed to be: the Head of the divine kingdom. That kingdom had burst upon them unawares.