In Eph. 3:1-3 βthe dispensation of the grace of Godβ is specifically called βthe mysteryβ (i.e., secret). It is thus designated for two reasons:
1β£ It had been βkept secret since the world began, but now,β through Paul, had been βmade manifestβ (Rom. 16:25). βIn other agesβ it was βnot made knownβ (Eph. 3:5). Rather, βfrom the beginning of the worldβ it had been βhid in Godβ (Ver. 9), βhid from ages and from generations, but nowβ¦ made manifest to His saintsβ (Col. 1:26).
2β£ It was at the same time the explanation, the key, to all Godβs good news, including that which had been proclaimed in ages past. It explained how it was that Abel could be declared righteous by bringing an animal sacrifice, βGod testifying of his giftsβ (Heb. 11:4), how Noah could become βan heir ofβ¦ righteousnessβ by building an ark (Heb. 11:7), how anyone could be saved under the dispensation of the Law, and how it is that we can be saved today by grace through faith alone.
Thus we have in Paulβs epistles, not only the gospel [good news] of βthe secretβ (Eph. 3:1-3), but at the same time, βthe secret of the gospelβ (Eph. 6:19,20).
This great secret, revealed to and through Paul, has rightly been called the capstone of divine revelation, for it concerns Godβs eternal purpose in Christ. Through Paul, the chief of sinners saved by grace, God has now made this glorious secret known to us (Eph. 1:9) that we, in turn, might make it known to others (Eph. 3:9). source
[β¦] now that the secret of Godβs great plan has been made known, how much more reason there is toΒ studyΒ the Scriptures with a view to [β¦]