John Lightfoot on Luke 17:20

[The kingdom of god cometh not with observation.] The kingdom of God, or of heaven, hath especially a twofold distinct sense in the Holy Scriptures. In some places it signifies the propagation of the gospel by the Messias and his followers, and that especially amongst the Gentiles: in other places it denotes the Messiah's victory and vengeance upon the Jews, the enemies of this gospel; but in the Jewish schools this was their conceit of him: that when he came he should cut off all those nations that obeyed not his, i.e., the Jewish law; redeeming Israel from the Gentile yoke; establishing a kingdom and age amongst them that should be crowned with all kind of delights whatever. In this they were miserably deceived, that they thought the Gentiles were first to be destroyed by him, and then that he himself would reign amongst the Israelites. Which, in truth, fell out just contrary; he was first to overthrow Israel, and then to reign amongst the Gentiles.

It is easy to conceive in what sense the Pharisees propounded that question, When the kingdom of God should come? that is, when all those glorious things should be accomplished which they expected from the Messias? and, consequently, we may as well conceive, from the contexture of his discourse, in what sense our Saviour made his reply: "You inquire when the Messias will come: His coming will be as in the days of Noah, and as in the days of Lot. For as when Noah entered the ark the world perished by a deluge, and as when Lot went out of Sodom those five cities were overthrown, 'so shall it be in the day when the Son of Man shall be revealed.'" So that it is evident he speaks of the kingdom of God in that sense, as it signifies that dreadful revenge he would ere long take of that provoking nation and city of the Jews. The kingdom of God will come when Jerusalem shall be made like Sodom, verse 29, when it shall be made a carcase, verse 37.

It is plain to every eye, that the cutting-off of that place and nation is emphatically called his kingdom, and his coming in glory. Nor indeed without reason: for before he wasted the city and subverted that nation, he had subdued all nations under the empire and obedience of the gospel; according to what he foretold, "That the gospel of the kingdom should be preached in all the world, and then should the end [of Jerusalem] come." And when he had obtained his dominion amongst the Gentiles, what then remained towards the consummation of his kingdom and victories, but to cut off his enemies the Jews, who would not that he should rule over them? Of this kingdom of God he speaks in this place, not answering according to that vain apprehension the Pharisee had when he propounded the question, but according to the thing itself and the truth of it. There are two things he saith of this kingdom:

1. That it comes not with observation. Not but that it might be seen and conspicuous, but that they would not see and observe it. Which security and supineness of theirs he both foretells and taxeth in other places once and again.

2. He further tells them, this kingdom of God is within you: you are the scene of these triumphs. And whereas your expectancies are of that kind, that you say, Behold here a token of the Messias in the subduing of such a nation, and, Behold there in the subduing of another; they will be all in vain, for it is within you; within, and upon your own nation, that these things must be done. I would lay the emphasis in the word you, when commonly it is laid in within.

Besides, those things which follow, verse 22, do very much confirm it, that Christ speaks of the kingdom of God in that sense wherein we have supposed it: they are spoken to his disciples "that the days will come, wherein they shall desire to see one of the days of the Son of man, but shall not see it." The days of the Son of man, in the Jewish style, are the days of the Messias: days, wherein they promise themselves nothing but pleasing, prosperous, and gay enjoyments: and, questionless, the Pharisees put this question under this notion only. But our Saviour so applies the terms of the question to the truth, and to his own purpose, that they signify little else but vengeance and wrath and affliction. And it was so far from it, that the Jews should see their expected pleasures, that the disciples themselves should see nothing but affliction, though under another notion.