Here it is! Why Jesus will not come before the man of sin comes first:
2 Thess. 2:1-3
1Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him,2That ye be not soon shaken in mind, or be troubled , neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand .
3Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed , the son of perdition;