In this event, Jesus was talking to the Pharisees. How could God’s kingdom be in the hearts of Pharisees? Jesus had called the Pharisees hypocrites! (Read Luke 11 and Matthew 23.)
The NIV, ESV, CSB, NASB translate this as “the kingdom of God is among you.” These verses may be better rendered with the thoughts: “The kingdom of God comes not with outward show…the kingdom is among you.”
How would the kingdom be among them? Jesus, the King, was the representative of that kingdom and He was right there! The Pharisees were looking for a sign or some evidence of Jesus’ earthly kingdom, power, and authority. He told them he was the King of that kingdom. Though they didn’t believe him.
In the next verse, Jesus gave a fuller answer to His sincere disciples. He compared His kingdom to lightning (Greek “astrape” – bright shining – like the sun) which gradually brings light to the world. In verse 25 he further explained he first would need to suffer. His kingdom in power and glory would not be set up immediately.
Then in verses 26 through 28 he compares the days of Noah and Lot to the days of the Son of Man. As Noah and Lot were present during their days so the Son of Man will be present during his day. The world was ignorant of what was about to happen. They continued on with normal life activities. Comparing this to the parallel account in Matthew 24:37-39, this is the time of Jesus’ secret return. (See FAQ question on 1 Thessalonians 5:2 for a fuller explanation.)
Back to Luke 17, verses 29 and 30 compare Jesus’ revealing to the day the flood came and the day Sodom was destroyed. Revealing has the thought of disclosing something hidden. During the initial stage of his second advent, only believers will recognize his return. At the later or revealing stage, the world will know. Christ will be revealed to all through intense trouble. This then is the answer to the Pharisees question, “when the Kingdom of God should come.”
The flood and destruction of Sodom were literal but also symbolic pictures of a destruction of earth’s society. God promised He would not destroy society again with a flood. (Genesis 9:15) God will not destroy the literal earth. Remember: “the earth abides forever,” and “God himself that formed the earth and made it; he hath established it, he created it not in vain he formed it to be inhabited; I am the Lord and there is none else.” (Isaiah 45:17)
We look forward to Jesus’ earthly government which will be very different from current society. The scriptures style it “a new heaven and a new earth wherein dwells righteousness.” (2 Peter 3:13)