Albert Barnes on 1 Thessalonians 3:4

For verily, when we were with you, we told you before, etc. It is not mentioned in the history Acts 17 that Paul thus predicted that peculiar trials would come upon them, but there is no improbability in what is here said. He was with them long enough to discourse to them on a great variety of topics, and nothing can be more probable, than that, in their circumstances, the subjects of persecution and affliction would be prominent topics of discourse. There was every reason to apprehend that they would meet with opposition on account of their religion, and nothing was more natural than that Paul should endeavour to prepare their minds for it beforehand.

That we should suffer tribulation. We who preached to you; perhaps also including those to whom they preached.

Even as it came to pass, and ye know. When Paul, Silas, and Timothy were driven away, and when the church was so much agitated, by the opposition of the Jews, Acts 17:5-8.