‘For you know what commandments we gave you through the Lord Jesus'.
This defines what they had received. Direct commandments from the Lord Jesus, as found through the authority of the teaching of Jesus passed on through the Apostles, and through Paul, and the early church, the ‘Testimony of Jesus' (as later found in the Gospels). The word for ‘commandment' contains the idea of strict orders similar to military orders (Acts 16:23-24). We are under orders. It is not a matter of choice. So Paul stresses that he had not passed on his own ideas, they were the commands of the Lord.