To get the true meaning of what is meant here, it is important to look at the context.
34 Most certainly I tell you, this generation will not pass away until all these things are accomplished. 35 Heaven and earth will pass away, but my words will not pass away.
The term “pass away” has the meaning of to no longer exist:
34 Most certainly I tell you, this generation will not pass away until all these things are accomplished. 35 Heaven and earth will pass away, but my words will not pass away.
Looking at “Heaven and earth will pass away,” one can see that this is the end of the heaven and earth, of the time period being talked about.
Jesus references the days of Noah and how the flood came and took them (the wicked) away, in Matthew 24:37-39(WEB):
37 As the days of Noah were, so will the coming of the Son of Man be. 38 For as in those days which were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noah entered into the ship, 39 and they didn’t know until the flood came and took them all away, so will the coming of the Son of Man be.
The heavens and earth up to the flood were destroyed. But this symbolized the wicked. The physical earth and heavens remain. The wicked don’t. 2 Peter 3:5-7, 10-13 helps us to understand this and shows us that the wicked will be taken away again (destroyed) when Jesus returns:
5 For this they willfully forget that there were heavens from of old, and an earth formed out of water and amid water by the word of God, 6 by which means the world that existed then, being overflowed with water, perished. 7 But the heavens that exist now and the earth, by the same word have been stored up for fire, being reserved against the day of judgment and destruction of ungodly men.
10 But the day of the Lord will come as a thief in the night; in which the heavens will pass away with a great noise, and the elements will be dissolved with fervent heat, and the earth and the works that are in it will be burned up. 11 Therefore since all these things will be destroyed like this, what kind of people ought you to be in holy living and godliness, 12 looking for and earnestly desiring the coming of the day of God, which will cause the burning heavens to be dissolved, and the elements will melt with fervent heat? 13 But, according to his promise, we look for new heavens and a new earth, in which righteousness dwells.
Jesus told his disciples that the angels would take the wicked away (reap them) and destroy them. Notice how Jesus likens this to an end of an age. The wicked generation of Noah’s day was destroyed and so it will be when Jesus returns.
36 Then Jesus sent the multitudes away, and went into the house. His disciples came to him, saying, “Explain to us the parable of the darnel weeds of the field.”
37 He answered them, “He who sows the good seed is the Son of Man, 38 the field is the world, the good seeds are the children of the Kingdom, and the darnel weeds are the children of the evil one. 39 The enemy who sowed them is the devil. The harvest is the end of the age, and the reapers are angels. 40 As therefore the darnel weeds are gathered up and burned with fire; so will it be at the end of this age. 41 The Son of Man will send out his angels, and they will gather out of his Kingdom all things that cause stumbling and those who do iniquity, 42 and will cast them into the furnace of fire. There will be weeping and gnashing of teeth.
49 So will it be in the end of the world. The angels will come and separate the wicked from among the righteous, 50 and will cast them into the furnace of fire. There will be weeping and gnashing of teeth.”
Looking back at Matthew 24:34-35, we see that the term “pass away” means to cease to exist. We can easily see how the heavens and earth are figurative and easily agree that Jesus’ words would not pass away. What about the phrase “this generation will not pass away until…?” Is this talking about the disciples of Jesus back then or perhaps today?
34 Most certainly I tell you, this generation will not pass away until all these things are accomplished. 35 Heaven and earth will pass away, but my words will not pass away.
Could this be talking about Jesus’ disciples back then or today or both or something else?
The phrase “will not pass away until” denotes that there is a time of passing away, similar to the passing away of the heaven and earth. We know that the wicked passed away in the flood of Noah’s day and were symbolized as, “the world that existed then.” Jesus explained that Noah’s generation went on living their lives until the flood came. So it will be the same when Jesus comes. The wicked generation will be living their lives during this period of tribulation, until Jesus comes in power with his angels. The righteous are delivered. Those chosen to be part of the symbolic bride of Christ (the chosen ones) will be gathered by angels too as shown in Matthew 24:31. The nations will be given the opportunity to submit to Jesus as shown in Psalms 2. Revelation 21:1-4 shows God’s kingdom coming down to earth to bestow blessings on righteous mankind.
Jesus mentioned many things that will befall his disciples in the previous verses. It would be fitting to say that those things would happen first. Just as Jesus referenced Daniel while explaining the end times to his disciples, Daniel had put things in order too. In Matthew 24:3, Jesus’ disciples asked him three questions. The last question was about “the end of the age.” The end of the age is not complete until all the things prophesied occur.
3 As he sat on the Mount of Olives, the disciples came to him privately, saying, “Tell us, when will these things be? What is the sign of your coming, and of the end of the age?”
32-35 “Take a lesson from the fig tree. From the moment you notice its buds form, the merest hint of green, you know summer’s just around the corner. So it is with you: When you see all these things, you’ll know he’s at the door. Don’t take this lightly. I’m not just saying this for some future generation, but for all of you. This age continues until all these things take place. Sky and earth will wear out; my words won’t wear out.
34 I assure you, the end of this age will not come until all I have spoken comes to pass. 35 The earth and sky will wear out and fade away before one word I speak loses its power or fails to accomplish its purpose.”
In conclusion, the “generation” that will not pass away (until all the events that Jesus stated would have to happen first) is talking about the wicked people to be destroyed when Jesus comes in power with his angels. Jesus’ arrival in power is likened to the flood’s arrival in power. There was a dramatic separating work then and will be.
Compare: Understanding the difference between the coming and arrival of the kingdom of God
Compare: What happens with Jesus’ coming, arrival, and the end of the age?