Did Paul teach that the day of the Lord was at hand, or that it was not?

The key word in 2 Thessalonians 2:2 is the Greek enestēken, from enistēmi. Paul uses the same verb for ‘things present’ as against ‘things to come’ (Romans 8:38), and for “this present evil world” (Galatians 1:4). So most modern translations take the false message to be that the day had already come: the WEB has “the day of Christ has already come”, and the BSB “that the Day of the Lord has already come”. On that reading someone had told the Thessalonians, perhaps in a letter falsely bearing Paul’s name (2:2), that the day had arrived and they were living in it. Some older scholars, Thayer among them, took the word to mean ‘is impending’, as the KJV’s ‘is at hand’ does. Either way, Paul’s answer is the same: that day will not come until the falling away and the man of sin come first (2:3).

That does not contradict his first letter, which never says the day was due within a set time. It says the day will come “as a thief in the night” (1 Thessalonians 5:2), suddenly and without warning, so believers must stay awake and ready. ‘We which are alive’ (4:15) groups Paul with whichever believers are living when the Lord comes; he names no date and does not claim to be one of them. Elsewhere he just as readily counts himself among the dead who will be raised: God “will also raise up us by his own power” (1 Corinthians 6:14). In both letters the day is certain, sudden and still to come.

Paul hoped to live to see it

Some scholars, Christians among them, think Paul at first hoped to be alive at the Lord’s return, and later expected to die first (2 Timothy 4:6). Even so, a hope is not a promise. Neither letter sets a date, and the first letter speaks of believers living with Christ “whether we wake or sleep” (1 Thessalonians 5:10).

Christians differ over whether Paul personally expected to live until the Lord’s return, and over who or what “withholdeth” the man of sin (2 Thessalonians 2:6–7). Neither question changes the answer above.