Adam Clarke's Commentary on the Bible

Verse 3 (2 Thessalonians 2:3)

Except there come a falling away first - We have the original word αποστασια in our word apostasy; and by this term we understand a dereliction of the essential principles of religious truth - either a total abandonment of Christianity itself, or such a corruption of its doctrines as renders the whole system completely inefficient to salvation. But what this apostasy means is a question which has not yet, and perhaps never will be, answered to general satisfaction. At present I shall content myself with making a few literal remarks on this obscure prophecy, and afterwards give the opinions of learned men on its principal parts.

That man of sin - Ὁ ανθρωπος της ἁμαρτιας· The same as the Hebrew expresses by און איש ish aven , and בליעל איש ish beliyaal ; the perverse, obstinate, and iniquitous man. It is worthy of remark that, among the rabbins, Samael, or the devil, is called און ואיש בליעל איש ish beliyaal veish aven , the man of Belial, and the man of iniquity; and that these titles are given to Adam after his fall.

The son of perdition - Ὁ υἱος της απωλειας· The son of destruction; the same epithet that is given to Judas Iscariot, John 17:12 ; (note). The son of perdition, and the man of sin, or, as some excellent MSS. and versions, with several of the fathers, read, ανθρωπος της ανομιας , the lawless man, see 2 Thessalonians 2:8 , must mean the same person or thing. It is also remarkable that the wicked Jews are styled by Isaiah, Isaiah 1:4 , משחיתים בנים benim mashchithim , "children of perdition;" persons who destroy themselves and destroy others.

- Adam Clarke's Commentary on the Bible