Albert Barnes Commentary 2 Thessalonians 2:5

"Remember ye not, that, when I was yet with you, I told you these things?" — 2 Thessalonians 2:5 (ASV)

Remember ye not, that, when I was yet with you, I told ye these things? The whole subject of the second advent of the Saviour seems to have constituted an important part of the instructions of Paul when at Thessalonica. He now refers them to what he had told them respecting the great apostasy, to show that his views had not changed, and that he did not mean them to understand that the world would soon come to an end. He had stated these things to them, implying that a considerable interval must elapse before the Saviour would appear.

Much of the obscurity of this prophecy arises from the fact that the apostle alludes to things which he had told them when with them, of which we now have no knowledge. Hence, what would have been perfectly clear to them on reading this letter is now difficult to understand.