When Christ returns, this happens immediately, sudden destruction, and the earth is gone.
His return means our salvation and the judging of the world in righteousness by the man God has appointed, Jesus Christ.
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2 Peter 3
10 But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.
11 Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness,
12 Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat?
13 Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness.
14 Wherefore, beloved, seeing that ye look for such things, be diligent that ye may be found of him in peace, without spot, and blameless.
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Hebrews 9
24 For Christ is not entered into the holy places made with hands, which are the figures of the true; but into heaven itself, now to appear in the presence of God for us:
25 Nor yet that he should offer himself often, as the high priest entereth into the holy place every year with blood of others;
26 For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself.
27 And as it is appointed unto men once to die, but after this the judgment:
28 So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.
The first time Christ came, was as an offering for sin, the second time to save us from the wrath of God on this world, which is that sudden destruction and the judgment that Paul described in Acts 17. Notice this warning of coming judgment is an important message to the unbelieving world.
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Acts 17
21 (For all the Athenians and strangers which were there spent their time in nothing else, but either to tell, or to hear some new thing.)
22 Then Paul stood in the midst of Mars' hill, and said, Ye men of Athens, I perceive that in all things ye are too superstitious.
23 For as I passed by, and beheld your devotions, I found an altar with this inscription, TO THE UNKNOWN GOD. Whom therefore ye ignorantly worship, him declare I unto you.
24 God that made the world and all things therein, seeing that he is Lord of heaven and earth, dwelleth not in temples made with hands;
25 Neither is worshipped with men's hands, as though he needed any thing, seeing he giveth to all life, and breath, and all things;
26 And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation;
27 That they should seek the Lord, if haply they might feel after him, and find him, though he be not far from every one of us:
28 For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring.
29 Forasmuch then as we are the offspring of God, we ought not to think that the Godhead is like unto gold, or silver, or stone, graven by art and man's device.
30 And the times of this ignorance God winked at; but now commandeth all men every where to repent:
31 Because he hath appointed a day, in the which he will judge the world in righteousness by that man whom he hath ordained; whereof he hath given assurance unto all men, in that he hath raised him from the dead.
32 And when they heard of the resurrection of the dead, some mocked: and others said, We will hear thee again of this matter.
33 So Paul departed from among them.
34 Howbeit certain men clave unto him, and believed: among the which was Dionysius the Areopagite, and a woman named Damaris, and others with them.