V.1-11 The life which Paul lived was exactly the same as the one they were called upon to bear; a life of joyful hope and hard labor. He wasn’t telling them doctrine, but pointing out what will be the results of having received the doctrine of Christ. The doctrine we learn in these two books concerns the details of the two future comings of the Lord Jesus.
V.12 The happy Christian life is one of constant watchfulness, though God may sometimes give us pleasant circumstances. But these people were mostly suffering persecution for their faith. Sometimes we get criticized by other believers when we stand firmly, as these Thessalonians did.
V.13 They had not received the message as if it came from Paul, but as the Word of God. And notice it says that it works when we believe it! How much do we really believe it? And our life is showing how much we believe. The Word of God is the source of all our confidence.
V.14-20 Persecutions, which were caused by Satan hindering Paul, means that he was not able to see them face to face. But he accepted that as being allowed by God.
V.19-20 But this very hindrance made him think of when they all would be together with Christ in heaven. Notice how the believers, as well as Christ, filled his heart with joy. We often just think of being with Christ, but we are going to bring joy to each other as well.