"Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him, 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. 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; 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" (2Thes.2:1-4).
"Remember ye not, that, when I was yet with you, I told you these things"(2Thes.2:5)?
"And now ye know what withholdeth that he might be revealed in his time. For the mystery of iniquity doth (does)already work: (Note: 1John.2:18-19; 4:1-4) only he who now letteth will let, until he be taken out of the way. And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming."
A. The beast / antichrist "revealed in his time" (42 months)
And they worshiped the dragon which gave power unto the beast: and they worshiped the beast, saying, Who is like unto the beast? who is able to make war with him? And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months, i.e. 3½ years (Rev.13:4-6). 
1. Everything associated with the beast belongs in his time period (42 Months)
a. The false prophet
"And I beheld another beast (false Prophet Rev.19:20) com- ing up out of the earth...he exerciseth all the power of the first beast before him, (antichrist Rev.13:12) and causeth
the earth and them which dwell therein to worship the first beast, whose deadly wound was healed. And he doeth great wonders...And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast saying to them that dwell on the earth." (Rev 13:11-14) This beast is identified as the "false prophet." (Rev.19:20; 13:11-18)
b. Mystery Babylon the Great, the Mother of Harlot
I will shew unto thee (you John) the judgment of the great whore that sitteth upon many waters...So he carried me away in the spirit into the wilderness: and I saw a woman sit upon a scarlet coloured beast, full of names of blasphemy, having seven heads and ten horns.
"These have power to shut heaven, that it rain not in the days of their prophecy: and have power over waters to turn them to blood, and to smite the earth with all plagues, as often as they will. And when they shall have finished their testimony, the beast that ascendeth out of the bottomless pit shall make war against them, and shall overcome them, and kill them", (the two witnesses are killed by the beast) (Rev.11:6-13).
d. The Seven last plagues
"And I heard a great voice out of the temple saying to the seven angels, Go your ways, and pour out the vials of the wrath of God upon the earth. And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men which had the mark of the beast, and upon them which worshipped his image (Rev.16:1-2). "And the fifth angel poured out his vial upon the seat of the beast; and his kingdom was full of darkness; and they gnawed their tongues for pain..." (Rev.16:10)