Judgement Day

Judgment Day, as understood in Christianity, is the final time of reckoning, when God will judge the entire world for its sins, and will appropriately send all the gays, atheists, lady ministers, heathens in general, and godbotherers straight to Hell. It forms part of the overall Christian eschatology that will end either with the total destruction of the Earth, or with total peace on Earth (believers seem to have a hard time agreeing on what will actually happen, especially to the earthly realm).

The concept of a final judgement of all people is not unique to Christianity, though the particular Christian version has some unique features. Zoroastrianism, some 400-600 years older than Christianity, and Christianity's fellow-Abrahamic faith Islam, some 600 years younger, both have quite similar concepts, which are likely related. The general concept of a final judgment before a final destruction of the Earth features in some ancient Greek and African religions, as well as in several examples from India and China.

Zoroastrian connection
Like a large number of Christian concepts including Heaven and Hell as well as sin (at least as Christians understand the concept), the concept of the "Final Judgment" is likely influenced by the Zoroastrian religion. After the final 3000 year cycle, a "Last Savior" will be born to a virgin, the seed of the Zoroaster, and upon the final savior's death, all of the dead (those in both Heaven and Hell) will rise from the dead and will be judged. Those in Hell who have redeemed themselves of sin will be allowed into Heaven, and those in Heaven who are no longer worthy will find themselves in Hell. It would be hard to argue that the Christian concept is not a direct retelling of this myth, in a Jewish framework.

Christian belief
In ancient Judaism, there was little concept of an afterlife; Heaven and Hell did not exist. The discussions of "end times" in Judaism foreshadowed much of how Christians understand the Final Judgment &mdash; minus the "judgment". They believed God would return to his people, the Temple would (once again) be rebuilt, and that all of the dead would rise in praise of God.

Christianity starts there, then says that God will judge each person according to their sins, allowing only those deemed worthy to remain with him in Heaven. Every person, including every single person who has ever lived and died, will be rejoined with his/her physical body. It is this physical body that goes to heaven, if worthy. The rest would go to a literal "Hell" or a figurative "Hell on Earth". Roman Catholics say that all who are in Heaven will remain in Heaven, those in Hell will remain in Hell, while some Evangelicals claim the times until such day comes would be spent respectively in Paradise and Sheol instead and after having been judged the people in the former going to Heaven and those in the latter to Hell, perhaps prompting one to ask why such a worldwide event is even necessary.

While the idea of Last Judgment is in no way extra-biblical, most of the writings in the Bible, including the 4 Gospels and Paul's letters, assumed the Final Judgment would be immediate, generally within their lifetimes or at most, the lifetime of their children. Revelation is the text that really suggests this would be a futuristic event. It is also the mythic text from which most artistic representations of the Final Days are pulled.

Jesus, especially in the non-canonical works, appears obsessed with Final Days and Final Judgment. While Jesus does not say exactly when this will happen he does clearly say that it will be in the lifetime of those hearing his sermons:

Verily I say unto you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.

Verily I say unto you, All these things shall come upon this generation. Verily I say unto you, This generation shall not pass, till all these things be fulfilled.

Nevertheless I say unto you, Hereafter shall ye see the Son of man sitting on the right hand of power, and coming in the clouds of heaven.

Verily I say unto you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.

Verily I say unto you, That there be some of them that stand here, which shall not taste of death, till they have seen the kingdom of God come with power.

Verily I say unto you, that this generation shall not pass, till all these things be done.

And ye shall see the Son of man sitting on the right hand of power, and coming in the clouds of heaven.

But I tell you of a truth, there be some standing here, which shall not taste of death, till they see the kingdom of God.

Verily I say unto you, This generation shall not pass away, till all be fulfilled.

Paul similarly believes the end time is close at hand:

But this I say, brethren, the time is short: it remaineth, that both they that have wives be as though they had none.

Hath in these last days spoken unto us by his Son…

But now once in the end of the world hath he appeared to put away sin by the sacrifice of himself.

Who verily was foreordained before the foundation of the world, but was manifest in these last times for you.

But the end of all things is at hand.

Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time.

It is clear from these quotes that both Jesus and Paul felt the end time was right around the corner.

Islamic mythology
There is a concept of a Last Judgment in Islam but Muslims can't agree exactly what will happen.

Social effects
Christians, especially the Religious Right, use the fear of Final Judgment in their rhetoric, both about the way humans should behave, as well as justifications for their own actions, especially any anti-environmental position they hold. Famous "pastors" from the fundamentalists' side of Christianity, like Fred Phelps and Benny Hinn, routinely bring up Final Judgment in their castigation of modern society.

In context with the mythology of the Final Judgment and Final Days, there is a move amongst fundamentalists to go to Israel and help resettle Palestine (regardless of the fact that this resettlement is illegal, or that there are people already living there) because they believe the language of Revelation that suggests the End of the World will come when the Temple is rebuilt and the lands resettled by the Israelite.