According to 1 Thessalonians 4:16-18, and 1 Corinthians 15:51-54; Christ will return for His church before the tribulation, taking all of His believers off the earth to heaven, this is called the rapture. When this occurs, the Holy Spirit, working through the church, will be removed from the earth, which according to 2 Thessalonians 2:6-7 is currently restraining the anti-christ. God will call His own witnesses (Revaltion 11:1-14, 14:6-13) to preach the gospel and save new believers to Christ. 

Regarding those who did not believe in Christ before the rapture and took pleasure in wickedness  2 Thessalonians 2:8-12, says; 8 Then that lawless one will be revealed whom the Lord will slay with the breath of His mouth and bring to an end by the appearance of His coming; 9 that is, the one whose coming is in accord with the activity of Satan, with all power and signs and false wonders, 10 and with all the deception of wickedness for those who perish, because they did not receive the love of the truth so as to be saved. 11 For this reason God will send upon them a deluding influence so that they will believe what is false, 12 in order that they all may be judged who did not believe the truth, but took pleasure in wickedness. NASB.