In Christianity heaven is being in the presence of God with places prepared for the faithful by Jesus and is viewed as eternal bliss beyond that which can currently be known. Those who are allowed into heaven are said to be given new bodies that do not decay and death will be gone. Marriage is not a part of heaven. It is also possible there are different 'levels' of heaven. The conditions to enter heaven in Christianity, (the state of "salvation"), often revolve around some standard of piety achieved through knowing Jesus.
The essence of heaven
Though there is much conjecture about what Heaven is like, its central core is that we will be with Jesus Himself. He has entered back into the presence of the Father and has conveyed to us that the redeemed of the Lord will likewise be with Him where He is. Paradise may be to Heaven as the foyer may be to the inner room of a great Mansion. Without a doubt, Jesus responded to the penitent thief on the cross who turning to Him and said "Remember me Lord, when you come in Your Kingdom", saying, "I tell you most definitly, today, you will be with me in Paradise". He also said, "Where I am, there you will be also." And speaking of the time that we will be in the presence of Jesus, John the Apostle says, "We shall be like Him, for we shall see Him as He really is."
With regard to what Heaven actually looks like, little information is given, and it is likely that the reality is beyond earthly comprehension. Artistic depictions of Heaven are usually characterized by bright, shining light; Dante's Paradiso is an example, although the overwhelming light there is at least partly a metaphor for divine love.
Catholicism and Orthodox Christianity
In Orthodox and Catholic Christianity, belief in Jesus and proper works are often considered necessary and go hand in hand. Sins of earth must first be cleansed through Purgatory before one can enter heaven. In some versions sufficient good deeds can lead to entering heaven even without belief in Jesus if one never had the chance to know about Jesus, such as pious Jews who died prior to the coming of Jesus.
In Protestant Christianity there is no one standard, but most denominations were started with the understanding that salvation comes from belief in Jesus and acceptance of Him as a "personal Lord and Savior". This doctrine is know as Sola fide. Luther summed it up as salvation by faith alone. Much of Protestant and Catholic views can overlap with Catholics emphasizing good works and Protestants emphasizing a relationship with Jesus - which then shows its 'fruits' through good works, although purgatory is usually not a concept that Protestant churches follow. Anglicans, who have a theology and church practice similar to Catholics, take a view very close to the view taken by Catholicism. Some Protestants, such as Calvinists, believe that salvation is pre-destined by God. Those He has chosen will follow Him. Still others are universalist and hope that eventually everyone will enter heaven (although some of purging of sins may be necessary).
Jehovah's Witnesses teach that God's Kingdom refers to more than merely a state of mind or heart. The Kingdom of God as taught by Jehovah's Witnesses, is an actual Kingdom, or government set up by Jehovah in Heaven, that will rule over the Earth after removing all current Kingdoms or Governments at Armageddon, which they teach as the meaining of Bible verses such as (Daniel 2:44). Jehovah's Witnesses teach that Jesus Christ is the King of this Kingdom and as such has had all authority in heaven and on earth delegated to him by his God and Father Jehovah which they teach is what Jesus meant at (Matthew 28:18). They teach that only Jehovah God himself has more authority then Jesus Christ and they draw this belife from Bible verses such as (1 Corinthians 15:27-28)
The Kingdom of God, to Jehovah's Witnesses, is made up of 144,000 other Kings which belive are numbered at (Revelation 7:4) and also at (Revelation 14:1) as Spiritual Israel and that these rule with Jesus, but under his direct control, and are the only humans that will take part in a very special resurrection known as the First Resurrection, of which those raised cannot die, as they are raised as spirit creatures and ascend to Heaven to rule as Kings. They base this belief on thier interpretation of Bible verses such as (Revelatio 20:4-5). Jehovah's Witnesses believe that God's Kingdom began ruling in the year 1914, which they arrive at by using what is termed as Reliable Bible Chronology.
Jehovah's Witnesses believe that since 1914 the world has seen the most destructive Wars, diseases, food shortages and natural disasters over any other period in human history because Satan the Devil was thrown from Heaven to the Earth in that year. They believe that this made Satan very angry and since then "Woe" has been on the earth. They use (Revelation 12:7-8,12) to support this, as well as teach that Satans being cast to the Earth is the reason for the Great Tribulation spoken of by Jesus and the Prophet Daniel in the Bible at (Daniel 12:1) and also (Matthew 22:21-22).
Jehovah's Witnesses teach that the sons of Israel, or biological Jews, were initially given the exclusive privilege of being the only people selected to rule as Kings in The Kingdom of God, which they teach is the meaning of (Exodus 19:5-6), but that they lost this privilege by breaking Gods covenant and killing the Messiah upon his arrival which they teach as the meaning of Jesus words at (Matthew 8:12). They teach that gentiles, or Non-Jewish people, are now being chosen to fill those same Kingly positions as Spiritual Israel Via the New covenant which they teach is the meaning of (Romans 9:6), and not biological Israel via the Law Covenant. Jehovah's Witnesses also support this belief with scriptures such as (Matthew 21:43) and also (Luke 20:9-19).
The Kingdom of God, as taught by Jehovah's Witnesses, will destroy and replace all existing kingdoms and governments during Armageddon, and rule the earth from heaven for one thousand years, which they teach is the meaning of Bible verses like (Daniel 2:44) and (Revelation 20:6). They believe it will create the paradise on earth that Adam and Eve lost in the Garden of Eden, Which they teach is described in the Bible at (Psalms 37:29) and spoken of by Jesus at (Matthew 5:5) as well as John at (Revelation 21:1-4). During this thousand year reign, they teach that all righteous and unrighteous humans will be resurrected from the dead in perfect human bodies. Jehovah's Witnesses teach that this is the "Second Resurrection", and only occurs during total Kingdom rule. They teach that these ones can die again if their deeds, during the thousand years, are not in line with Gods rule, which they teach is John's meaning at (Revelation 20:13).
Jehovah's Witnesses teach that Satan the Devil will be imprisoned during this one thousand year reign, and unable to influence humans in any way under the Kingdoms rule, which they teach is the meaning of (Revelation 20:1-2). They teach that All human beings that do not submit fully to the Kingdom of God during this thousand year reign of Christ will die before the thousand years is over which they take (Isaiah 17:1,20) to mean. This Jehovah's Witnesses teach is the "Second Death", from which there is no resurrection, which they teach is the meaning of (Revelation 20:14).
Jehovah's Witnesses teach that after the last rebellious humans, and Satan are destroyed that Jehovah and his Kingdom will rule forever over a perfect human race, on a paradise earth completely free from sin, death, and any wicked influences whatsoever. It will not be passed on to anyone as no one will grow old and die in heaven or on earth.
Jehovah's Witnesses teach that the Kingdom of God is the central theme of the entire Bible, Jesus message while on earth, and their own door to door preaching. They teach that their door to door preaching is a major "Sign of the End" before the Kingdom brings to an end this worlds system of governments. In this way, they believe, Gods Will shall be done in Heaven and also on the Earth and further make Gods name, Jehovah ,Holy, or sanctified.
Judaism focuses much less on the nature and method of entering heaven, for which the Old Testament says little, but emphasize good deeds (mitzvot) on this earth and generally follows univeralist tendencies. Even Orthodox Jews rarely discuss the afterlife which is seen as unimportant, instead putting more emphasis on Philosophy, Mysticism, and especially Ethics.
Islam emphasizes belief in God and acceptance of Muhammed as God's Prophet. There is also a physical component not found in Christianity and Judaism. Amongst certain fringe, fundamentalist sects of contemporary Islam, if one dies in Jihad, no matter how bad he had been during his life, he is immediately lifted to heaven and given 72 virgins. This view is emphasized among Islamic militant extremists (terrorists), who believe it applies to them when they kill "infidels" who they believe stand in the way of Islam.