The last days (also referred to as the End Time or the Great Tribulation) is a period of roughly 3 1/2 years or 42 months (Revelation 11:2 - 3) that will shortly come upon the entire earth. It will a time, just before Jesus' Second Coming, when the Beast and the False Prophet will rule the world through their counterfeit version of God's kingdom.
The 42 months (1,260 days, see Revelation 11:3, 12:6) of the last or final period before Jesus return can further be divided into two relatively distinct pieces. The first piece is about two years (24 months) in length. The second or last piece, Biblically called "the day of the Lord" (Isaiah 2:12, Joel 2:11, 2Peter 3:10), is about 18 months in duration. This second part of the great tribulation represents God's direct punishment of unrepentant humanity.
The Apostle Paul warned his friend Timothy about the time before the return of Christ when he wrote, "Know this also, that in the last days perilous times shall come" (2Timothy 3:1, HBFV unless stated). Peter also warned the church regarding the state of the world near its end when he said, "Knowing this first, that in the last days there will come mockers, walking according to their own personal lusts" (2Peter 3:3).
Preparation of the world
The Bible lists several events, some taking many years until they fully mature, which will directly lead to the great tribulation period. Humanity, in the last days, will increasingly adopt a negative attitude toward God's laws and reject keeping them, opting instead to doing whatever they decide is right. This lawlessness, which at its core is selfish and self-centered, will cause people to greatly lack mercy, forgiveness and love (Matthew 24:9 - 10, 12).
The world will experience an increased frequency of wars, rumors of wars, earthquakes, famines and still more calamities (Matthew 24:6 - 7). Many false prophets will appear and deceive the masses with false hopes (Matthew 24:4 - 5, 11, 26 - 27). Deception, in general, will be rampant.
Many who considered themselves Christians and believers in the true God will also abandon their beliefs in the last days (2Thessalonians 2:1 - 3). A temple will be built in Jerusalem just before the public appearance of the Beast, False Prophet and the Two Witnesses. It will be in the temple that the "abomination of desolation" will declare that he is god in the flesh and demand he be worshipped (Matthew 24:15, 2Thessalonians 2:1 - 4, Revelation 11:1 - 3, 13:8, 12, 15).
Why is it so bad?
Why are the last days of man the worst time humanity will ever experience (Matthew 24:21)? One reason is that it will force ALL humans to choose one of two options - both of which bring pain and suffering. No one will be allowed to go "undecided" for very long!
Choosing to obey and worship the Beast during the last days will forestall the devil's wrath and allow people to live a little bit longer on earth. It comes, however, at the tremendous expense of experiencing horrific punishments from God (Revelation 14:9 - 10). Choosing to obey the Eternal, however, will spare people his wrath (see Revelation 9:4, 18:4). They will, however, be considered enemies of the world, hunted down and martyred (Revelation 6:11, 7:14, 13:7 - 10, 15).
The Great Tribulation begins
Satan the devil will launch his second but last offensive in heaven in the hope he can wrest control of the universe away from God. He and his evil army will, however, be defeated by righteous angels. They will be cast back down to earth and permanently banned from heaven (Revelation 12:7 - 10). This complete rejection causes the full force of Satan's wrath to come upon the earth for a short period of time (1,260 days).
A unique paradox will exist during the time of Satan's visible rule on earth. On the one hand, Christians will be persecuted and killed in great numbers while others will be made to serve the devil's agenda. It will be the greatest period of trial and temptation the world ever has or will ever see (Matthew 24:21). Yet, on the other hand, in the last days many people will grow rich and prosperous. In fact, the merchants and businesses who got incredibly wealthy through the new one world system will mourn when it is finally destroyed (Revelation 18:9 - 19)!
The Revealing of Satan
The Beast and the False Prophet begin their work of deceiving man and ruling the earth under the direct inspiration of the Devil (Revelation 13:3 - 15). God's Two Witnesses also begin their ministry of confronting these powerful individuals and calling upon all those on the earth to repent of their sins before the imminent return of Christ (Revelation 11:3 - 7).
A Place of Protection
Some (but not all) Christians are miraculously taken by God to an earthly "place of safety" or protection (not a rapture) for the duration of the Tribulation (Revelation 12:6, 14, 13:5). They will be protected from the horrors of Satan's world-ruling government. Those protected in the last days will be kept physically alive until they are changed to immortal spirit beings during the short period of Jesus' Second Coming (1Thessalonians 4:16 - 17, 1Corinthians 15:51 - 53).
Mark of the Beast
Soon after the Beast and False Prophet take control over the world, they demand all humans receive a "mark." This mark symbolizes a person's willingness to worship the Beast and obey the new one world system. Those who refuse to accept the mark of the Beast will not only be unable to buy or sell anything, they will be hunted down for their disobedience and killed (Revelation 13:14 - 17).
Martyrdom of Saints
In spite of what many religious organizations teach, not all Christians are whisked away in some secret rapture to be protected from the devil's wrath. The Bible clearly states that not only will true believers exist on the earth during man's last days, many of them (most? all?) will reject the Beast's mark. This will make them targets for persecution, which will ultimately lead to their martyrdom (Matthew 24:9, Revelation 6:11, 12:11, 17, 13:7, 14:12 - 13).