4 We have confidence in the Lord about you, that you are doing and will continue to do what we command. CSB
“We have confidence in the Lord about you” The phrase suggests that Paul and the rest of the brothers (Christians) were convinced that they are true believers in Jesus Christ.
“that you are doing and will continue to do what we command.” The commands (that is the gospel and also new revelation received from the Holy Spirit…John 16:13) that were handed down to the church in Thessalonica from Paul and the Apostles. It was derived from Jesus’s instruction to His disciples in Matthew 28:20 to pass down to those who were going to get saved to keep them and to put them into practice.