Albert Barnes Commentary 1 Thessalonians 4:2

"For ye know what charge we gave you through the Lord Jesus." — 1 Thessalonians 4:2 (ASV)

For you know what commandments. It was only a short time Paul was with them, and they could not fail to remember the rules of living which he had laid down.

By the Lord Jesus. By the authority of the Lord Jesus. Some of those rules, or commandments, the apostle probably refers to in the following verses.