I thought Scripture teaches the Rapture can't happen until the apostasy comes first and the man of lawlessness is revealed. So how can you say that the Church will be gone before the beginning of Tribulation?
Your interpretation of the Bible is in error. The Bible never connects the Rapture to the coming apostasy or the arrival of the Antichrist (i.e., the man of lawlessness). On the contrary, the Bible consistently teaches that the Lord’s return to His Church is imminent and dependent on nothing:
Matt. 24:42 “Therefore be on the alert, for you do not know which day your Lord is coming.
Mark 13:32 “But of that day or hour no one knows, not even the angels in heaven, nor the Son, but the Father alone.
Mark 13:33 “Take heed, keep on the alert; for you do not know when the appointed time will come.
We believe you are misunderstanding Paul's teaching taken from 2Thessalonians 2:
2Th. 2:1 Now we request you, brethren, with regard to the coming of our Lord Jesus Christ and our gathering together to Him,
2Th. 2:2 that you not be quickly shaken from your composure or be disturbed either by a spirit or a message or a letter as if from us, to the effect that the day of the Lord has come.
2Th. 2:3 Let no one in any way deceive you, for it will not come unless the apostasy comes first, and the man of lawlessness is revealed, the son of destruction,
2Th. 2:4 who opposes and exalts himself above every so-called god or object of worship, so that he takes his seat in the temple of God, displaying himself as being God.
Paul says that the “day of the Lord” cannot come to pass "unless the apostasy comes first, and the man of lawlessness is revealed.” The term “day of the Lord” is a reference to the seven-year Tribulation, not to the Rapture.