(NASB) Luke 17:31 “On that day…”
  Jesus told His disciples how He would come again and what people can expect.
(NASB) Luke 17:24 “For just like the lightning, when it flashes out of one part of the sky, shines to the other part of the sky, so will the Son of Man be in His day.”

  Jesus will be seen by all the world.  He will reveal Himself so all will see Him at the same time.  How will this be?  I don’t know.  But Jesus never deceives, lies nor misleads.
  When Jesus comes it will be sudden, unexpected and with His coming – His judgment.

  Just as in the days of Noah (Luke 17:26-27), the people had been forewarned about the flood and we have been forewarned today.  Just as in the days of Noah, people did not listen nor believe what Noah preached then and people do not believe God’s coming judgment today.  

  Just as in the days of Lot (Luke 17:28-29), people were judged by God for sinning against Him.  It is so in our day also as it was then:
(NASB) Romans 1:28 “And just as they did not see fit to acknowledge God any longer, God gave them over to a depraved mind, to do those things which are not proper…”

  Listen to these words of warning of God’s coming judgment:
(NASB) 2 Peter 2:4-10 “For if God did not spare angels when they sinned, but cast them into hell and committed them to pits of darkness, reserved for judgment;
5 and did not spare the ancient world, but preserved Noah, a preacher of righteousness, with seven others, when He brought a flood upon the world of the ungodly;
6 and if He condemned the cities of Sodom and Gomorrah to destruction by reducing them to ashes, having made them an example to those who would live ungodly lives thereafter;
7 and if He rescued righteous Lot, oppressed by the sensual conduct of unprincipled men
8 (for by what he saw and heard that righteous man, while living among them, felt his righteous soul tormented day after day by their lawless deeds),
9 then the Lord knows how to rescue the godly from temptation, and to keep the unrighteous under punishment for the day of judgment,
10 especially those who indulge the flesh in its corrupt desires and despise authority.”

  When Jesus comes again, He will be seen by all the people on planet earth.  How?  God knows!  When Jesus comes again He will come to judge all who have rejected Him and refused to acknowledge their need of Him.
  When Jesus comes again, it will be just as in the days of Noah and Lot.  Judgment was on all who had spurned the preaching of Noah and rejected righteous Lot. 
  When Jesus comes again it will be sudden, unexpected and seen by all.

(NASB) Luke 17:30 “It will be just the same on the day that the Son of Man is revealed.”