The "Day of Judgment" is a future event promised in Scripture where God will bring about final justice and condemnation on all those who are still in their sins while delivering those who are in Christ into the joys of eternal life. It is the day on which God will sentence unbelievers to eternal torment in hellfire while preserving the repentant who believe on Jesus Christ solely on the basis of the sacrificial work of Jesus on their behalf through His death on the cross for sin.
What is the Day of Judgment?
Most of the New Testament writers who refer to the day of judgment by name seem to assume that the reader already knows what it is. In the Gospel of Matthew, for example, Jesus says things like:
"Then He began to denounce the cities in which most of His miracles were done, because they did not repent. 'Woe to you, Chorazin! Woe to you, Bethsaida! For if the miracles had occurred in Tyre and Sidon which occurred in you, they would have repented long ago in sackcloth and ashes. Nevertheless I say to you, it will be more tolerable for Tyre and Sidon in the day of judgment than for you. And you, Capernaum, will not be exalted to heaven, will you? You will descend to Hades; for if the miracles had occurred in Sodom which occurred in you, it would have remained to this day. Nevertheless I say to you that it will be more tolerable for the land of Sodom in the day of judgment, than for you," (Matthew 11:20-24).
He does not define the day. He assumes that His audience already knows what it is. Yet, even here, there are important clues about this day. It is clearly a future day of great importance. What's more, the people of ancient Sodom and Gomorrah from way back in the time of Abraham, the people of Tyre and Sidon "long ago," and the people of the towns of Chorazin and Bethsaida of Jesus' own day would all stand together to be judged on this same day of judgment. So, even if this were all we had to go on, we would pretty easily come to the conclusion that we are talking about a final day of judgment before God upon all people of all times.
Jesus and the New Testament authors seem to have largely felt no need to explicitly define the day of judgment because it was language already well-known in their day. The phrase "day of judgment" occurs rather frequently in Jewish writings of the New Testament era and before, such as in the apocalyptic Esdras literature, where we read:
"But the day of judgment will be the end of this age and the beginning of the immortal age to come, in which corruption has passed away, sinful indulgence has come to an end, unbelief has been cut off, and righteousness has increased and truth has appeared. Therefore no one will then be able to have mercy on someone who has been condemned in the judgment, or to harm someone who is victorious," (2 Esdras 7:113-115, NRSV).
Or in the apocryphal Book of Judith, which states:
"Woe to the nations that rise up against my people! The Lord Almighty will take vengeance on them in the day of judgment; he will send fire and worms into their flesh; they shall weep in pain forever," (Judith 16:17, NRSV).
Still, when Paul is preaching in Athens to a pagan, gentile audience with no background in Jewish thought, he does explicitly explain:
"Therefore having overlooked the times of ignorance, God is now declaring to men that all people everywhere should repent, because He has fixed a day in which He will judge the world in righteousness through a Man whom He has appointed, having furnished proof to all men by raising Him from the dead," (Acts 17:30-31).
Peter, likewise, uses rather vivid language in his second letter, writing:
"Know this first of all, that in the last days mockers will come with their mocking, following after their own lusts, and saying, 'Where is the promise of His coming? For ever since the fathers fell asleep, all continues just as it was from the beginning of creation.' For when they maintain this, it escapes their notice that by the word of God the heavens existed long ago and the earth was formed out of water and by water, through which the world at that time was destroyed, being flooded with water. But by His word the present heavens and earth are being reserved for fire, kept for the day of judgment and destruction of ungodly men," (2 Peter 3:3-7).
The language of complete judgment over all creation and the comparison to the flood of Noah give us a powerful picture of the complete extent of this judgment. We likewise know from Jude that this will be a day when not only men but also fallen angels are judged:
"And angels who did not keep their own domain, but abandoned their proper abode, He has kept in eternal bonds under darkness for the judgment of the great day," (Jude 6).
Peter is, however, clear that the godly will be rescued on this day while the wicked are left to destruction:
"the Lord knows how to rescue the godly from temptation, and to keep the unrighteous under punishment for the day of judgment, and especially those who indulge the flesh in its corrupt desires and despise authority," (2 Peter 2:9-10).
The Means of Escape
The day of judgment is a serious matter of great importance in Scripture. Paul urgently warns:
"But because of your stubbornness and unrepentant heart you are storing up wrath for yourself in the day of wrath and revelation of the righteous judgment of God, who will render to each person according to his deeds," (Romans 2:5-11).
Yet He also points to our way of escape:
"For while we were still helpless, at the right time Christ died for the ungodly. For one will hardly die for a righteous man; though perhaps for the good man someone would dare even to die. But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Much more then, having now been justified by His blood, we shall be saved from the wrath of God through Him," (Romans 5:6-9).
The death of Christ has delivered those who believe from judgment and condemnation. We likewise read in the Gospel of John:
"As Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up; so that whoever believes will in Him have eternal life. For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life. For God did not send the Son into the world to judge the world, but that the world might be saved through Him. He who believes in Him is not judged; he who does not believe has been judged already, because he has not believed in the name of the only begotten Son of God," (John 3:14-18).
It is not our efforts, but rather through looking in faith to Christ and His sacrifice that we are saved from condemnation and judgment. John goes on to write in his first letter:
"Whoever confesses that Jesus is the Son of God, God abides in him, and he in God. We have come to know and have believed the love which God has for us. God is love, and the one who abides in love abides in God, and God abides in him. By this, love is perfected with us, so that we may have confidence in the day of judgment; because as He is, so also are we in this world. There is no fear in love; but perfect love casts out fear, because fear involves punishment, and the one who fears is not perfected in love. We love, because He first loved us," (1 John 4:15-19).
God loved us by sending His Son, Jesus Christ, to take our punishment and die on our behalf. If we confess that Jesus is, indeed, the Son of God and believe on this great act of love by God for us, we can have confidence on the day of judgment. What's more, His love will become our love. Receiving His love, we ourselves will love as He does and thus turn from sin to righteousness and from selfishness to self-sacrifice for others. So in this age and in the age to come, Christ alone is the answer.