Better beguile; since the word means not only making a false impression, but actually leading astray. Except there come a falling away. Before except insert in translation the day shall not come. Such ellipses are common in Paul.
Falling away (ἀποστασία)
Only here and Act 21:21. Comp. lxx, Jos 22:22; 2Ch 29:19.
The man of sin - the son of perdition (ὁ ἄνθρωπος τῆς ἀνομίας, ὁ υἱὸς τῆς ἀπωλείας)
See on children of light, 1Th 5:5. The phrase man of sin (lawlessness) does not occur elsewhere, either in N.T. or lxx. Son of perdition is found Joh 17:12, olxx: τέκνα ἄπωλείας children of perdition (A.V. transgression), Isa 57:4. The man of sin has been thought to refer to Caligula, Titus, Simon Magus, Nero, the Pope of Rome, Luther, Mahomet, etc.