The apostle Paul is an extraordinary teacher and mentor. He constantly reminds us to have a joy that will hold up to all of the difficulties and challenges that life can bring. This is not hypothetical teaching- Paul displays joy even while he is imprisoned for the very faith that gives him that joy. And he warns against letting anyone place barriers that would hinder us from finding that same strong joy that comes through faith in Jesus. 

Reference: Philippians 3:1-11 (NLT)