What did Jesus mean when He said, "The kingdom of God is within you" (Luke 17:21, KJV)?

We will now turn to Luke 17. (Read verses 20 to 37.) The Pharisees demanded, when the kingdom of God should come. The Lord replies to them, "The kingdom of God cometh not with observation … the kingdom of God is within you" (among you, see the margin). But immediately thereupon, the Lord turned to his disciples, and told them of a coming which should be of universal observation. "For as the lightning that lighteneth out of the one part under heaven, shineth unto the other part under heaven; so shall also the Son of Man be in his day." Here then a two-fold coming of the kingdom is distinctly intimated; the one not with observation, or outward show; (see margin;) the other to be visible as the lightning, unto all. To the Pharisees the Lord would speak only of the former: "Behold the kingdom of God is among you" — the king stands among you even now — already he is come; but you will not receive him. The kingdom assuredly was not within those Pharisees. Their condemnation was, that they would not receive it. Only by being converted could they enter it. But repent they would not. Therefore the Lord tells them nothing further as to the kingdom. The disciples however were informed as to the coming of the kingdom; but the Son of Man must first suffer and be rejected. Then would ensue a period which would resemble the days of Noah, and the days of Lot. Until Noah went into the ark, and the flood came, the world went on carelessly in sin. Until Lot went out of Sodom, and the fire and brimstone fell from heaven, the inhabitants of that city ran greedily in the depths of wickedness. Even thus, said the Saviour, will the world do, until "the day when the Son of Man shall be revealed." Can there be an intervening period of a thousand years of universal righteousness? Impossible. "And as it was in the days of Noah, so shall it be also in the days of the Son of Man. They did eat, they drank, they married wives, they were given in marriage, until the day that Noah entered into the ark, and the flood came, and destroyed them all. Likewise also as it was in the days of Lot; they did eat, they drank, they bought, they sold, they planted, they builded; but the same day that Lot went out of Sodom, it rained fire and brimstone from heaven, and destroyed them all. Even thus shall it be in the day when the Son of Man is revealed." During those days, true disciples would desire to see the return of their Lord; but for a while their hopes would not be realized. Then if any man should say unto them, "See here; or see there," they must not hearken to such deceivers. For false Christs and false prophets should arise ever and anon, through the period during which the Lord should remain away. But whatever these deceivers might pretend; whether they should say, he is in the city, or he is in the desert; disciples are told not to "go forth," nor "follow," them. The advent, when it took place, would be visible to all — visible as the vivid lightning's startling flash. It would be a revelation through the clouds of heaven. In that day, it would be of no avail to flee in this direction or in that; for whether in bed, or grinding at the mill, or in the open field, the taking and the leaving would inevitably take place. The judgments of that fearful day would as surely take away all those that "do iniquity," as the waters of the flood took all the guilty inhabitants of the world in the days of Noah. just as the flood took away all except the few that the ark preserved — preserved in order to the re-peopling of the earth — so will the judgments, like a second flood, at the return of Jesus, take all away but a remnant, who shall form the nucleus of the millennial population of the earth. Some shall be "left" then, even by the judgments of that great day. The world therefore does not come to an end when the second advent takes place. There is a people "left" still; and the millennium ensues.

In the next verses, from verse 20 to 37, the question was actually raised as to the coming of God's kingdom. The Pharisees asked when it should come, and the Lord places them on their plain responsibility. "The kingdom of God cometh not with observation," or outward show. It should not be said, Lo here! or Lo there! for that kingdom then was there among them. The King was speaking to them. Ought they not to have known Him because He came in grace? If He had humbled Himself to know their sorrows and to die for their sins, was that a reason for not discerning His greatness and moral perfection manifested in ten thousand ways? Did not His holy love to the poor and guilty prove, plainly enough, who He was? If man's heart had not been opposed to all that was the delight of God in the kingdom, if his eye had not been blind to all that was lovely and of good report, he would have felt that the lower Christ stooped, the more wonderful were His works.