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. Who opposeth and exalteth - He stands against and exalts himself above all Divine authority, and above every object of adoration, and every institution relative to Divine worship, σεβασμα, himself being the source, whence must originate all the doctrines of religion, and all its rites and ceremonies; so that sitting in the temple of God - having the highest place and authority in the Christian Church, he acts as God - taking upon himself God's titles and attributes, and arrogating to himself the authority that belongs to the Most High.
The words ως Θεον, as God, are wanting in ABD, many others, Erpen's Arabic, the Coptic, Sahidic, Ethiopic, Armenian, the Vulgate, some copies of the Itala, and the chief of the Greek fathers. Griesbach has left them out of the text, and Professor White says, Certissime delenda; "They should most certainly be erased." There is indeed no evidence of their being authentic, and the text reads much better with out them: So that he sitteth in the temple of God, etc.