Summary: 1) The dual source of his apostolic authority (Ephesians 1:1a), 2) A dual description of believers (Ephesians 1:1b), 3) A dual blessing for believers (Ephesians 1:2a), and 4) The dual source of those blessings (Ephesians 1:2b).
If you are a fan of the game show: " Who Wants to Be a Millionaire? ", you may be familiar with a recent contestant named Justin. He said: "I got to $250,000. It was a life-changing sum. It was mine, and I could’ve walked away with it. But I was never going to walk away. Before the show I had promised myself that I wouldn’t act tentatively—that I would answer the questions on stage as if I were sitting at home, with no money on the line. I had come to a soundstage in Stamford, Connecticut, to play the game, and, God help me, I was going to play it until I reached either damnation or glory. I didn’t get to glory. When I lost $225,000 in a single second, it was like a needle had been pushed through my cerebral cortex, pinning me to the spot of my failure. I walked off stage in a daze, my mind still affixed to that cataclysmic moment. I didn’t know the answers to most of my questions with absolute certainty, but they were all written in such a way that I could figure them out. The trick was to trust my instincts, and not let self-doubt force a premature exit". (http://news.nationalpost.com/2015/02/06/i-went-on-who-wants-to-be-a-millionaire-and-lost-225000-in-10-seconds-it-almost-ruined-me/
The book of Ephesians is written to Christians who might be prone to treat their spiritual resources much like Justin treated his financial resources. Such believers are in danger of suffering from spiritual malnutrition, because they do not take advantage of the great storehouse of spiritual nourishment and resources that is at their disposal. This beautiful letter tells Christians of their great riches, inheritances, and fullness in Jesus Christ and in His church. It tells them what they possess and how they can claim and enjoy their possessions. The first three chapters of Ephesians emphasize doctrine, and the last three chapters emphasize behavior. The first half is theological, and the second half works out that theology in practical ways. The letter to the Ephesians is a marvellously concise, yet comprehensive, summary of the Christian good news and its implications. Nobody can read it without being moved to wonder and worship, and challenged to consistency of life (Stott, J. R. W. (1979). God’s new society: the message of Ephesians (p. 15). Downers Grove, IL: InterVarsity Press.).
The greatest resources that we possess are useless if we don't use them. If we don't know what they are, how to access them and effetely utilize them at critical junctures, then we risk living shallow, meaningless lives. Through the book of Ephesians and this beginning section in particular, the Apostle Paul is going to introduce us to the resources that are available to use.
In his salutation, Paul presents the dual resources of Grace and Peace through 1) The dual source of his apostolic authority (Ephesians 1:1a), 2) A dual description of believers (Ephesians 1:1b), 3) A dual blessing for believers (Ephesians 1:2a), and 4) The dual source of those blessings (Ephesians 1:2b).