Difficult things happen: in Genesis we see Joseph being sold into slavery, and in Philippians Paul is writing as a prisoner for the gospel. In God's great plan, their hard circumstances served great purpose in furthering His salvation plan. Paul says in his letter, "I want you to know..." He wants us to know that the gospel is being advanced, and that we are partners in His great purpose. The more we understand this, the more we can rejoice and celebrate what God is going to accomplish.