This was according to the eternal purpose that he has realized in Christ Jesus our Lord,  in whom we have boldness and access with confidence through our faith in him. (ESV)
A few years ago a pastor on staff at a large church that will remain un-named said the following:
"I just want to encourage everyone of us to realize when we obey God we're not doing it for God. I mean, that's one way to look at it. Were doing it ourselves. Because God takes pleasure when we're happy. That's the thing that gives him the greatest joy this morning. I want you to know this morning just do good for your own self. Do good cuz God wants you to be happy.. When you come to church when you worship him you're not doing it for God really. You're doing it for yourself because that's what makes God happy. Amen?"
I have news for the woman who said this. And I have news for you. God does not find the most pleasure when we act selfishly. He finds pleasure in accomplishing his eternal purpose and being glorified. Paul tells us in verse 11 of Ephesians 3 that God's purpose is realized in Christ Jesus. He does not say that God's purpose is realized in you or I. We are recipients of God's great mercy. And the result is that God is glorified. God exists for God's glory. He is complete and sufficient without mankind. He redeemed us as a demonstration of his great love and for his glory.
This is why Paul can then tell us in verse 12 that we can have boldness and access with confidence through our faith in Him! It is about him, and not about us. The thought of coming into God's presence without the work of Christ on our behalf ought to terrify us to death. Our sin separates us and invites God's just wrath. Do we come boldly because its our turn to be happy, and after all, if we are happy, God is happy? NO! We come boldly only because of our faith in the one who has gained access for us. That access cost him his blood being shed at the cross. The wrath we deserved was placed upon his back.
God has an eternal purpose. It is to be glorified. You are not his eternal purpose. Christ Jesus being glorified is his eternal purpose. Be very careful not to fall for the lie that it's all about you. There are many "Christians" who have caused themselves and a lot of other people a lot of hurt because they act selfishly.
Are you living to fulfill your purpose? Instead, how can you discover God's purpose and find true fulfillment by living for his glory? Why do you obey him? Is it for you? Or for Him?