Matthew 24:27 talks of the Son of Man (Jesus Christ) coming back like a flash of lightning.

Mat 24:27  For as the lightning comes from the east and flashes to the west, so also will the coming of the Son of Man be.

Luke 17:24 says something similar.

Luk 17:24  For as the lightning that flashes out of one part under heaven shines to the other part under heaven, so also the Son of Man will be in His day.

Are these verses saying that Jesus Christ will zip across the sky like lightning, or something else?  Let’s have a closer look by examining some of the Greek words.  Let’s look at Matthew 24:27 first.

Matthew 24:27

Mat 24:27  For as the lightning [astrape] comes from the east and flashes [phaino] to the west, so also will the coming of the Son of Man be.

The Greek word translated “lightning” is astrape, which means lightning, bright shining.  Here is an example where it is translated “bright shining”.

Luk 11:36  If then your whole body is full of light, having no part dark, the whole body will be full of light, as when the bright shining [astrape] of a lamp gives you light.”

The Greek word translated “flashes” (in Matthew 24:27) is phaino, which means shine.  Many translations have “shines” rather than “flashes”.

Lightning does not flash from east to west, rather it lights up the sky.  However, the sun moves from east to west.  A much better translation of Matthew 24:27 is this.

Mat 24:27  For as the bright shining (the sun) comes from the east and shines to the west, so also will the coming of the Son of Man be.

Indeed, Malachi 4:1-2 refers to Jesus Christ as “The Sun”.

Mal 4:1  “For behold, the day is coming, Burning like an oven, And all the proud, yes, all who do wickedly will be stubble. And the day which is coming shall burn them up,” Says the LORD of hosts, “That will leave them neither root nor branch.
Mal 4:2  But to you who fear My name The Sun of Righteousness shall arise With healing in His wings; And you shall go out And grow fat like stall-fed calves.

Let’s now look at Luke 17:24.

Luke 17:24

Luk 17:24  For as the lightning [astrape] that flashes [astrapto] out of one part under heaven shines [lampo] to the other part under heaven, so also the Son of Man will be in His day.

The Greek word translated “lightning” is astrape, the same word found in Matthew 24:27.  However, the Greek word translated “flashes” is astrapto, which means to flash as lightning, shine.  The only other place this word is used in Scripture is in Luke 24:4, where the women who came to Jesus’s empty tomb were met by angels.

Luk 24:4  And it happened, as they were greatly perplexed about this, that behold, two men stood by them in shining [astrapto] garments.

The Greek word translated “shines” (in Luke 17:23) is lampo, which means to beam, give light, and shine.  This verse could be translated as this.

Luk 17:24  For as the bright shining (the sun) that shines out of one part under heaven shines to the other part under heaven, so also the Son of Man will be in His day.

Either way, this verse tells us that Jesus Christ will light up the sky like lightning when He returns.  It doesn’t mention anything about speed.

Conclusion

Putting all these verses together we see that when Jesus Christ returns, His coming will be like the sun, a bright shining light that moves across the sky from east to west.  For more information see “What is ‘the sign of the Son of Man’ that appears in heaven, Mat 24:30?”