11This was according to the eternal purpose that he has realized in Christ Jesus our Lord, 12in whom we have boldness and access with confidence through our faith in him. 13So I ask you not to lose heart over what I am suffering for you, which is your glory.
This (the mystery of the Gospel being revealed) was done according to eternal purposes. So often we just look at things from the perspective of "what is going on now," or even worse, "what's in it for me." But there are purposes that are so much bigger we cannot begin to wrap our minds around them.
All things are created by Him and for Him. So if we even want to begin to try and understand something, that is where we start, Jesus Christ. Not ourselves. So now, we can approach an issue with confidence. Not because we will have all the answers, but because we know the starting point, the point by which all things are referenced.
If you build a building, and start in one corner, and that corner is off, the entire rest of the building is off, no matter how meticulous you are from then on. If our life is not built on the Rock, no matter how well we build, everything else is off. But if we know we have the correct starting point, we can continue in boldness and confidence.
Paul tells them not to lose confidence because he is suffering. In a sense, he is saying it is okay, everything is going according to plan, and in the end, I will be victorious. I say this so that you can be strengthened by what you see in me. Praise God.