Why hasn't the Antichrist been revealed yet?
Second Thessalonians 2:6-7 says: "And now ye know what withholdeth that he might be revealed in his time. For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way." Darkness cannot overtake the world because the Holy Spirit, which indwells every believer by faith, makes up the light of the world.
Also, the Great Tribulation is God's wrath on earth. To be more precise, Revelation 6:15-16 says the "wrath of the Lamb." That wrath does not come upon His Bride because Scripture guarantees: "For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ" (1st Thessalonians 5:9).