Ephesians 3
The 3rd chapter in Ephesians kind of sums up the first two chapters. In the first verses, Paul continues to emphasize that the 'Great Mystery' of God is that Christ came and made all people one under Him, meaning Jews and Gentiles. This was important for Paul to emphasize. Remember that it took a distict vision from God to Peter for him to go to Cornelius and stoning of Stephen to cause the believers to spread from Jerusalem, in order for the Gospel to be available to those other than Jews.
For many Jewish people (I think including many of the Apostles), there was this idea of a birthright of the Messiah. This thinking pervaded Jewish thought at the time and so it took a Paul, called distinctly to the Gentiles, and other events like the ones mentioned above to reveal this mystery that Christ came to redeem all mankind, not just those of Jewish origin.
In verse 6, Paul starts off by saying 'to be specific;' giving it emphasis so that the Ephesians don't miss that Christ made Gentlies fellow heirs and partakers of the promise in Christ Jesus through the gospel. Thank God He did that, or I know I'd be in trouble!

Tolkien imitates God?
Eph. 3:9-10: '...and to bring to light what is the administration of the mystery which for ages has been hidden in God who created all things; so that the manifold wisdom of God might now be made known through the church to the rulers and authorities in the heavenly places.'
God didn't reveal His full mystery to anyone, even the angels, until Christ came and rose again. It seems odd that He would withold this information from His most trusted servants. But I think it shows two things:
1. God is the only omniscient being and is the only one who knows all things.
2. Even the angels can't grasp the fullness of who God is and they are always learning new, cool stuff that makes God all the more awesome to them, too!

When I read this, I was reminded of the Silmarillion by JRR Tolkien. In his 'prelude' to Lord of the Rings, he explains the how Illuvatar(God) created things. First he created the 'Valar' and then the 'Maiar' which are basically angel type beings. Illuvatar uses them to sing the world into creation. He grants them the ability to see things in the future and how things will go, but it's not always a clear vision. They know that Elves and Men will be coming to earth, but they don't know when. So when the elves arrive in Middle-Earth and the Valar find them, they are amazed and in wonder at this new revelation from Illuvatar. They found that the elves were good and they praised Illuvatar for this new found aspect of who Illuvatar was.

Now, I'm not saying that because the angels didn't know that Christ and what He did for mankind was the great mystery of God, that we are for some reason better than the angels. Rather, what I'm saying is that when God revealed how He would redeem man to Himself through Christ, the angels were able to see the greatness, love and kindness of God in a way they had not experienced before. I think their reaction was awe, wonder and worship to their awesome God.

I don't think the angels will ever know exactly how if feels to have Christ redeem you to Himself, because they never strayed from Him when Satan fell. So we will have that special connection with God that no other part of God's creation can have or experience. Likewise, I don't think mankind will ever know the amazing experience of living in fellowship with God totally free from the effects of sin, like the angels do now. This is something that when we are with God for eternity, we can thank Him for the unique way that He revealed Himself to us, and through sharing that with each other, we will love and worship God even more!