11:17-20
The claim that Jesus was using demonic power was somewhat ridiculous, as a moment’s thought would show. If a kingdom was divided against itself then it could not have long to go before it would collapse. We should not expect the claims of opponents to have much logic to them. This includes the claims of so-called intellectuals. Atheism claims to be intellectually superior to theism, but atheism is actually self-contradictory. In short, if the claims of atheism are true, then the thoughts of atheism are worthless, so its claims are worthless. If you want a much fuller and well argued case for this then I strongly recommend the book Finding Truth by Nancy Pearcey.
Moreover, driving out demons was not an unknown enterprise, indeed the critics themselves did the same (though no doubt far less effectively!). So they brought criticism upon themselves.
So if Jesus was not driving out demons with demonic power, but by the “finger of God” then the kingdom of God was among them. That is what they should have been focusing on. So we see yet again that Jesus considered demonic activity to be real, and that one of the signs of the kingdom was the casting out of demons. We should expect the same to happen today.
11:21,22
It is interesting that in most accounts of casting out of demons the emphasis has been on the person who has been set free, eg the story of the demoniac with legions of demons. In this section (11:14-28) apart from a very brief mention in v14 all the emphasis is on the wider significance of the fact that Jesus has authority over demons, and has come to overturn their work (1 John 3:8). We have just seen those who claim Jesus was doing this by means of demonic power Himself. Jesus pointed out the ridiculousness of such a notion, then He said that the fact that demons are cast out is a sign that the kingdom of God is at hand. We now get further explanation of the significance. These two verses clearly view events as warfare, as a battle. The enemy, Satan, has possession of the earth and the people in it. Jesus has come to change things, and this involves overpowering the devil. There are two key aspects to this mentioned here. One is that Satan’s armour is overcome. The root of Satan’s power is our sin and the judgement we were under, but on the cross our sin and its debt were cancelled out, Satan’s hold over our life was broken. And people can now be brought from the kingdom of darkness to the kingdom of Jesus Christ (Col 1:13,14).