For from you the word of the Lord has sounded forth not only in Macedonia and Achaia but in every place your faith in God has gone forth, so that we have no need to say anything.
1 Thessalonians 1:8
In the same way a parent might have joy for what their son or daughter has accomplished, Paul takes pleasure and finds joy in what the Thessalonians are doing. He receives great joy that their faith has sounded forth to others. Their faith is a model for others and Paul is celebrating it. You can see the great joy he takes in knowing that his efforts of sharing his faith have produced such incredible fruit and impact.
There is a great joy in bringing someone far from God into a relationship with Jesus Christ. When we see the fruit of their changed life, we receive the joy of knowing that God has used us to make an eternal impact on others.
Take a moment to pray for a friend, a family member, or a co-worker who is far from God. Pray for an opportunity to invite her or him to Church.