In Philippians 1:10 (margin) Paul exhorts his readers to “Try (or test) things that differ” and in this book the author brings to the readers attentions the things that differ between the New Testament writings written during the Acts Period and those written afterwards.
In the book he exhibits that the mystery revealed after Acts 28:28 belongs to a dispensation different from that which obtained before Acts 28:28. This he does clearly and simply in three short chapters.
CHAPTER 1: THE MYSTERY, ITS RELATION TO ISRAEL AND THE GENTILES.
At Acts 28:28 Israel’s hope of the Lord’s return was deferred and salvation was sent unto the Gentiles, whereupon the Mystery was committed to Paul on behalf of the Gentiles and he suffered in making this hope known.
CHAPTER 2: THE MYSTERY, ITS CALLING AND HOPE.
The Mystery concerns our calling, to be seated together with Christ in the heavenly places far above all, and the one hope of our calling, to be manifested with Christ in glory.
CHAPTER 3: THE MYSTERY, ITS DISTINGUISHING CHARACTERISTICS.
The Mystery had been hidden from all ages until revealed through Paul after Acts 28:28, it occasioned a distinctive form of practise without the accompaniment of evidential gifts, and
the Mystery is that which God would make known to His Saints.
APPENDIX: PROGRESSIVE REVELATION
The three divisions of the New Testament