The seven-year Tribulation, also known as "Daniel's Seventieth Week" (Dan. 9:24-27) and "The Time of Jacob's Trouble" (Jer. 30:7), will be divided into two halves: three and one half years (Dan. 12:7); forty-two months (Rev. 11:2; 13:5); and twelve hundred sixty days (Rev. 11:3; 12:6). The purpose of the Tribulation is two-fold: it is God's effort to bring the lost of the world to repentance and salvation (2 Pet. 3:9; Rev. 9:20-21; 16:9-11). Note that these passages in Revelation occur in the two halves of the Tribulation: Ch. 6-11 and Ch. 13-18. But at the end of the seven years, the enemies of God will be destroyed by Christ's Second Coming (Rev. 19:11-21)!
God also uses the Tribulation to preform "eye surgery" on His blinded people, Israel (Rom. 11:7, 25; 2 Cor. 3:14; 4:4). Israel "blindly" (pun intended) enters into an agreement with the person they believe is their Messiah. For three and a half years, he keeps his word that Israel will experience peace, even though the world around it will be anything but peaceful (Dan. 9:27; Mt. 24:6). We read that during this time, the Gospel of the Kingdom will be proclaimed (note that it is not the Gospel that brings salvation, but it is merely the good news that Israel's Messiah has come to re-establish David's throne - Mt. 24:14). We might think of this period as a time when Israel has "severe cataracts" and is unaware of it.
Then, exactly in the middle of the seven-year peace agreement, their false messiah declares himself to be god, and demands all men worship him (Dan. 9:27; Mt. 24:15; Rev. 13-18). Israel realizes that their "savior" was not the Messiah. God opens their eyes to see that they are experiencing Daniel 9:27, and at last, they understand that the One the world had crucified had to be the true Messiah (Daniel 9:26 comes before 9:27)!
The one who impersonates the Messiah of Israel, guaranteeing their peace for seven years, is known by various names; he is "the Antichrist" (1 Jn. 2:18), "the Little Horn" (Dan. 7:8-25), "the Prince that shall come" (Dan. 9:26), "the Son of Perdition" and "the Man of Sin" (2 Thes. 2:3), "that Wicked One" (2 Thes. 2:8), and "the Beast" (Rev. 11:7; 13:1). In the end, he will simply be "the loser!"
There are none so blind, as those who refuse to see!