Matthew Poole and continuators on 1 Thessalonians 3:4

4 For verily, when we were with you we told you before that we should suffer tribulation , even as it came to pass, and ye know .

The Apostle having said that they knew they were appointed to sufferings, tells them here they knew it, because he had told them of it. Paul by some extraordinary instinct or Revelation often foresaw his sufferings, and God more generally told him of them at his first Conversion, Acts 9.16. And he told them of them that they might reckon upon sufferings. A faithful Minister will not only tell the people of the Crown, but of the Cross of Christ.

And what he foretold of his sufferings, he tells them came to pass, whereby they might be strengthened further in their Faith about the Gospel he had preached to them, and not be offended at his sufferings, being foretold to them, as well as appointed of God.