Paul rejoiced in his circumstances, because his circumstances strengthened the fellowship of the gospel. (v. 5)
Fellowship – def – to have in common. Christian fellowship is more than sharing a cup of coffee, lunch, passion for a sport, etc. Christian fellowship is about having Christ in common, the gospel in common, sharing Christ, sharing eternal life.

Paul told the Philippians that he had them in his mind, in his heart, and in his prayers.