The "End Times" is an extensive topic and a key, yet often misunderstood, passage in the discussion is Matthew 24, specifically verses 21-34.
For then there will be great distress, unequaled from the beginning of the world until now—and never to be equaled again. “If those days had not been cut short, no one would survive, but for the sake of the elect those days will be shortened. At that time if anyone says to you, ‘Look, here is the Messiah!’ or, ‘There he is!’ do not believe it. For false messiahs and false prophets will appear and perform great signs and wonders to deceive, if possible, even the elect. See, I have told you ahead of time. “So if anyone tells you, ‘There he is, out in the wilderness,’ do not go out; or, ‘Here he is, in the inner rooms,’ do not believe it. For as lightning that comes from the east is visible even in the west, so will be the coming of the Son of Man. Wherever there is a carcass, there these vultures will gather. “Immediately after the distress of those days “'the sun will be darkened, and the moon will not give its light; the stars will fall from the sky, and the heavenly bodies will be shaken.’“ "Then will appear the sign of the Son of Man in heaven. And then all the peoples of the earth will mourn when they see the Son of Man coming on the clouds of heaven, with power and great glory. And he will send his angels with a loud trumpet call, and they will gather his elect from the four winds, from one end of the heavens to the other.“Now learn this lesson from the fig tree: As soon as its twigs get tender and its leaves come out, you know that summer is near. Even so, when you see all these things, you know that it is near, right at the door. Truly I tell you, this generation will certainly not pass away until all these things have happened. Heaven and earth will pass away, but my words will never pass away.
An essential hermeneutic tool for understanding challenging passages such as these is to allow Scripture to interpret Scripture. Verse 34 of this passage gives context to interpret the preceding verses. "Truly I tell you, this generation will certainly not pass away until all these things have happened."
Many interpret this passage and Christ's coming in "power and glory" (v. 30) as a reference to The Second Coming. But when Jesus said he would be "coming back in power and glory", he did not mean his final coming or what is typically referred to as the Second Coming. Throughout the Bible, God came down to his people or manifested himself to Israel in many different ways for different purposes. One of these "coming" events was his coming to bring judgment on unfaithful Israel (i.e. Mic. 1:6-7) Likewise, Matthew 24:30 refers to Jesus coming back to judge Israel for their adulterous behavior and disregard for Jesus' teaching and warning while he was on the Earth, which eventually lead to his death on the cross. This specific coming in judgement came by way of the destruction of Jerusalem and the temple in AD 70. Furthermore, "these things", as referenced in verse 30, did indeed come within the generation (around 40 years) of the disciples that were present when he made this statement.
With Scriptures binding the text to keep "these things" within a generation, we now have a time and framework within which we can interpret the preceding verses such as verse 29, "The sun will be darkened and the moon will not give its light". Apocalyptic verses must be understood as symbolic in nature due to the fact that the Hebrew language and culture was as such. We know this by looking at other highly symbolic apocalyptic texts such as the book of Revelation. It is the most 'Hebraic' book in the New Testament, meaning it has more references and ties to the Old Testament than any other book. Therefore when we come to "End Times" imagery such as the complete darkening of the sun and moon we see that Old Testament language helps us understand this as hyperbolic symbolism rather than an actual observable event. For example, Isaiah 13:10-10
“For the stars of heaven and their constellations will not flash forth their light; the sun will be dark when it rises, and the moon will not shed its light. Thus I will punish the world for its evil, and the wicked for their iniquity; I will also put an end to the arrogance of the proud, and abase the haughtiness of the ruthless. I will make mortal man scarcer than pure gold, and mankind than the gold of Ophir. Therefore I shall make the heavens tremble, and the earth will be shaken from its place at the fury of the Lord of hosts in the day of His burning anger.”
There are similar thoughts, words and symbolism in these passages in Isaiah that mirror the language used in Matthew 24:29. This passage in Isaiah is a prophetic judgment of Old Testament Babylon which helps us understand the language that Jesus uses before his disciples as judgment language.
These few but important historical and Biblical points also help us in understanding the tribulation language that Jesus refers to starting in verse 21. Oftentimes verses 21-25 are used in reference to the Great Tribulation. Kept in context of the disciples were present at the time Jesus, this tribulation would be tied to the persecution and martyring of Christians in that generation prior to the destruction of AD 70 by Rome. Meaning the "Great Tribulation" described in this passage of scripture has already passed and the destruction of the temple was that tribulation which physically ended the Old Covenant (old Hebraic system) and solidified the New Covenant. Although the Christian today is not still awaiting Jesus' description of tribulation according to Matthew 24, we do not neglect the fact that followers of Christ will face tribulation or persecution to a certain extent in this age. There are other New Testament scriptures that pertain to this topic (Jm. 1:2-3; Matt. 5:10-12; 1 Pt. 4:12-16).