In order to best understand what Matthew 24:27 means, it is best to read this passage in context. For context, I will start at verse 1 and go through verse 28:
Jesus came out from the temple and was going away when His disciples came up to point out the temple buildings to Him. 2 And He said to them, “Do you not see all these things? Truly I say to you, not one stone here will be left upon another, which will not be torn down.”
3 As He was sitting on the Mount of Olives, the disciples came to Him privately, saying, “Tell us, when will these things happen, and what will be the sign of Your coming, and of the end of the age?”
4 And Jesus answered and said to them, “See to it that no one misleads you. 5 For many will come in My name, saying, ‘I am the Christ,’ and will mislead many.6 You will be hearing of wars and rumors of wars. See that you are not frightened, for those things must take place, but that is not yet the end. 7 For nation will rise against nation, and kingdom against kingdom, and in various places there will be famines and earthquakes. 8 But all these things are merely the beginning of birth pangs.
9 “Then they will deliver you to tribulation, and will kill you, and you will be hated by all nations because of My name. 10 At that time many will fall away and will betray one another and hate one another. 11 Many false prophets will arise and will mislead many. 12 Because lawlessness is increased, most people’s love will grow cold. 13 But the one who endures to the end, he will be saved. 14 This gospel of the kingdom shall be preached in the whole world as a testimony to all the nations, and then the end will come. 15 “Therefore when you see the abomination of desolation which was spoken of through Daniel the prophet, standing in the holy place (let the reader understand),16 then those who are in Judea must flee to the mountains. 17 Whoever is on the housetop must not go down to get the things out that are in his house.18 Whoever is in the field must not turn back to get his cloak. 19 But woe to those who are pregnant and to those who are nursing babies in those days! 20 But pray that your flight will not be in the winter, or on a Sabbath. 21 For then there will be a great tribulation, such as has not occurred since the beginning of the world until now, nor ever will. 22 Unless those days had been cut short, no life would have been saved; but for the sake of the elect those days will be cut short. 23 Then if anyone says to you, ‘Behold, here is the Christ,’ or ‘There He is,’ do not believe him. 24 For false Christs and false prophets will arise and will show great signs and wonders, so as to mislead, if possible, even the elect. 25 Behold, I have told you in advance. 26 So if they say to you, ‘Behold, He is in the wilderness,’ do not go out, or, ‘Behold, He is in the inner rooms,’ do not believe them. 27 For just as the lightning comes from the east and flashes even to the west, so will the coming of the Son of Man be. 28 Wherever the corpse is, there the vultures will gather.
Here, Jesus is speaking to His disciples (verses 1-4). Furthermore, He is speaking of the end times (verses 5-14). He speaks of the abomination of desolation, the tribulation and the many false Christs and false prophets that will arise (verses 15-24). Jesus notes He has told His disciples this in advance (verse 25). He warns of what these false Christs/prophets may say (verse 26). We then get to verse 27, which states, “For just as the lightning comes from the east and flashes even to the west, so will the coming of the Son of Man be.” This verse is not speaking of a Chinese woman that will be coming, as the cult Eastern Lightning claims (I briefly wrote about that cult here). In fact, when dealing with verses that are hard to interpret, it is good to remember that Scripture interprets Scripture. Luke 17:24 represents a good cross-reference for this verse. That verse, speaking of the same subject matter as Matthew 24:1-28, states, “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.” Basically, Jesus’ coming is going to come in a flash at a time we do not expect (Luke 12:40). Therefore, we should be ready for it (see also Matthew 24:29-51).