Who opposes and exalts himself above all that is called God, or that is worshiped; so that he as God sits in the temple of God, showing himself that he is God.
All Commentaries on 2 Thessalonians 2:4 Go To 2 Thessalonians 2
Ambrosiaster
AD 400
so much so that he sits in the temple of God
Thus it appears that he will either be of the circumcision or at least circumcised himself, so that the Jews will have the confidence to believe in him.
presenting himself as if he were God
He will even sit in Christ's seat in the house of God and declare that he is not the Son of God, but God himself.