This is the body of Christ working well - working out of love and out of selflessness and concern for each other! Paul and the other leaders had planted a church in Thessalonica and they were anxious that perhaps the hardships of persecution had caused them to give up faith. So they sent Timmy to check in on them and hear back that the Thessalonians have actually succeeded in keeping a strong community of faith and love! Paul is clearly overjoyed and relieved by this news. You can feel the deep concern and love in his letter to the people.