The falling away is a defection from Truth. It means that when satan is cast to earth as anti ('instead of') CHRIST, that people will fall away to satan, believing he is JESUS. The people defect to satan because they are ignorant of GOD'S WORD.
2Th 2:1 Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him,
2Th 2:2 That 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.
2Th 2:3 Let 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;
2Th 2:4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
And how many will defect?
Rev 17:8 The beast that thou sawest was, and is not; and shall ascend out of the bottomless pit, and go into perdition: and they that dwell on the earth shall wonder, whose names were not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is.
'wonder' in Rev 17:8 means to admire, the same as worship.
So, everyone on earth except those that had their names written in The Book Of Life at the foundation of the world will fall away.
And who had their names written in the Book Of Life from the foundation of the world?
Eph 1:4 According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
Eph 1:5 Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will,
And who are these people? They are the Elect. They stood against satan in the age that was and they will stand against him in this age also.
1Pe_1:2 Elect according to the foreknowledge of God the Father, through sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ: Grace unto you, and peace, be multiplied.
They are the people who know Truth.
Mat_24:24 For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
Good thing it's not possible!
And good thing it won't last for that whole seven years!
Mar_13:20 And except that the Lord had shortened those days, no flesh should be saved: but for the elect's sake, whom he hath chosen, he hath shortened the days.
