Who in what temple?
Matthew 12:3 But he said unto them, Have ye not read what David did, when he was an hungred, and they that were with him; 12:4 How he entered into the house of God, and did eat the shewbread, which was not lawful for him to eat, neither for them which were with him, but only for the priests? 12:5 Or have ye not read in the law, how that on the sabbath days the priests in the temple profane the sabbath, and are blameless? 12:6 But I say unto you, That in this place is one greater than the temple. 12:7 But if ye had known what this meaneth, I will have mercy, and not sacrifice, ye would not have condemned the guiltless. 12:8 For the Son of man is Lord even of the sabbath day.
John 5:39 Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me. 5:40 And ye will not come to me, that ye might have life. 5:41 I receive not honour from men. 5:42 But I know you, that ye have not the love of God in you. 5:43 I am come in my Father's name, and ye receive me not: if another shall come in his own name, him ye will receive.
2 Thessalonians 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; 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. 2:5 Remember ye not, that, when I was yet with you, I told you these things? 2:6 And now ye know what withholdeth that he might be revealed in his time.
Temples in...the Temple of God...
Matthew 21:12 And Jesus went into the temple of God, and cast out all them that sold and bought in the temple, and overthrew the tables of the moneychangers, and the seats of them that sold doves,
Mark 14:49 I was daily with you in the temple teaching, and ye took me not: but the scriptures must be fulfilled.
John 2:19 Jesus answered and said unto them, Destroy this temple, and in three days I will raise it up. 2:20 Then said the Jews, Forty and six years was this temple in building, and wilt thou rear it up in three days? 2:21 But he spake of the temple of his body. 5:14 Afterward Jesus findeth him in the temple, and said unto him, Behold, thou art made whole: sin no more, lest a worse thing come unto thee.
In the above, He, in "the temple of His body,...went into the Temple of God."
More temples
...in the Temple of God.
Luke 24:51 And it came to pass, while he blessed them, he was parted from them, and carried up into heaven. 24:52 And they worshipped him, and returned to Jerusalem with great joy: 24:53 And were continually in the temple, praising and blessing God. Amen.
Acts 2:1 And when the day of Pentecost was fully come, they were all with one accord in one place. 2:2 And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. 2:3 And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. 2:4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
2:46 And they, continuing daily with one accord in the temple, and breaking bread from house to house, did eat their meat with gladness and singleness of heart, 2:47 Praising God, and having favour with all the people. And the Lord added to the church daily such as should be saved.
Another one of The Spirit's temples goes into the Temple of God.
Acts 21:26 Then Paul took the men, and the next day purifying himself with them entered into the temple, to signify the accomplishment of the days of purification, until that an offering should be offered for every one of them.
The Apostle Paul was NOT referring to the man of sin in the temple of God (the Believer), rather in the Temple of God at Jerusalem.
Further, the Prophecy concerns events "in the holy place" at Jerusalem (located in what was then known as the southern province of Roman Judaea ).
Matthew 24:15 When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand: ) 24:16 Then let them which be in Judaea flee into the mountains:
Daniel 9:26 And after threescore and two weeks shall Messiah be cut off, but not for himself: and the people of the prince that shall come shall destroy the city and the sanctuary; and the end thereof shall be with a flood, and unto the end of the war desolations are determined.
He was referring to one coming in his own name as God Himself...
Not this...
Malachi 3:1 Behold, I will send my messenger, and he shall prepare the way before me: and the LORD, whom ye seek, shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in: behold, he shall come, saith the LORD of hosts.
But a counterfeit...
John 5:43 I am come in my Father's name, and ye receive me not: if another shall come in his own name, him ye will receive.
2 Thessalonians 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.
Why do they buy into his lie?
Because they are just like him. Just as he is ever high-fiving himself; they are ever high-fiving one another.
John 5:43 I am come in my Father's name, and ye receive me not: if another shall come in his own name, him ye will receive. 5:44 How can ye believe, which receive honour one of another, and seek not the honour that cometh from God only? 5:45 Do not think that I will accuse you to the Father: there is one that accuseth you, even Moses, in whom ye trust.
Luke 16:15 And he said unto them, Ye are they which justify yourselves before men; but God knoweth your hearts: for that which is highly esteemed among men is abomination in the sight of God.
Mark 13:14 But when ye shall see the abomination of desolation, spoken of by Daniel the prophet, standing where it ought not, (let him that readeth understand,) then let them that be in Judaea flee to the mountains:
Daniel 11:21 And in his estate shall stand up a vile person, to whom they shall not give the honour of the kingdom: but he shall come in peaceably, and obtain the kingdom by flatteries.
Daniel 11:32 And such as do wickedly against the covenant shall he corrupt by flatteries: but the people that do know their God shall be strong, and do exploits.