When Christ returned to put an end to the tribulation, He defeated all those who fought against Him.
“And I saw the beast (anti-Christ), the kings of the earth, and their armies, gathered together to make war against Him…Then the beast was captured, and with him the false prophet…These two were cast alive into the lake of fire…” Revelation 19:19-20
And the fate of the devils’ followers?
“And the rest were killed with the sword which proceeded from the mouth of Him (Christ)…And all the birds were filled with their flesh.”
Revelation 19:21
Interestingly, the devil wasn’t destroyed at this point, but was rather consigned to the bottomless pit which is the abode of fallen angels, i. e. demons. He would be confined to his prison all during the 1,000 year kingdom.
Because God wasn’t done with him yet.
Also, right before the beginning of the thousand years, all believers who were martyred during the tribulation were raised up to spend the thousand years reigning with Christ.
The deniers, however, will remain in their graves until the end of the thousand years.
At the end of the thousand years, God will release the devil so he can attempt to deceive all the unbelievers, i.e. those who will be born during the millennial kingdom. Only believers will enter the kingdom originally.
“Now when the thousand years have expired, Satan will be released from his prison and will go out to deceive the nations which are in the four corners of the earth…to gather them together to battle…” Revelation 20:7-8
God will quickly send fire from heaven to devour the devil and the deceived.
“The devil, who deceived them, was cast into the lake of fire and brimstone where the beast (anti-Christ) and the false prophet are. And they will be tormented day and night forever and ever.” Revelation 20:10
And then God will deal with unbelievers of all ages. All unbelievers will be resurrected to answer for their rebellion. Included will be those who thought they could earn their place in heaven by their good deeds, instead of accepting the free gift of grace made possible by the vicarious death of the Son of God. Those who accepted God’s free gift of grace were written in the Book of Life.
“And I (John) saw the dead, small and great, standing before God…And the dead were judged according to their works…The sea gave up the dead…and Death and Hades delivered up the dead who were in them…And anyone not found written in the Book of Life was cast into the lake of fire.”
Revelation 20:12-15
The Bible confirms that if a person attempts to earn heaven by good performance instead of accepting God’s free gift, that person must not be guilty of a single sin.
“…knowing that a man is not declared righteous by the works of the law but by faith in Jesus Christ…for by the works of the law no flesh shall be declared righteous (justified).” Galatians 2:16
And then Paul confirmed that a person attempting to please God must obey the whole law.
“For whoever shall keep the whole law, and yet stumble in one point, he is guilty of all.” James 2:10
The only One who was/is able to fulfill the whole law is the God/Man Jesus Christ.
Recall what Jesus said:
“Do not think that I came to destroy the Law…I did not come to destroy but to fulfill. For assuredly, I say to you, till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled.”
Matthew 5:17-18
Thus, after the thousand year kingdom and the devil is destroyed forever, there will be tremendous changes to the heavens and earth.
“…the heavens will pass away with a great noise, and the elements will melt with fervent heat; both the earth and the works that are in it will be burned up.” 2 Peter 3:10
And then the next step in God’s plan for the heavens and earth.
“Now I saw a new heaven and a new earth, for the first heaven and the first earth had passed away…” Revelation 21:1