Charles Ellicott Commentary Ephesians 1:9

"making known unto us the mystery of his will, according to his good pleasure which he purposed in him" — Ephesians 1:9 (ASV)

Having made known to us the mystery of his will.—In the same connection we read in 1 Corinthians 2:7, we speak the wisdom of God in a mystery. The word “mystery” properly signifies a thing which (Colossians 1:27) was hid from all ages, but is now made manifest.

So our Lord evidently uses it (Mark 4:11; Luke 8:10). For the rest, except in four passages of the Apocalypse (Revelation 1:20; Revelation 10:7; Revelation 17:5; Revelation 17:7), it is used by St. Paul alone, and by him no less than twenty-one times, of which ten belong to this Epistle and the parallel Epistle to the Colossians—always in connection with such words as “knowledge,” “declaration,” “dispensation.”

The ordinary sense of the word “mystery”—a thing of which we know that it is, though how it is we do not know—is not implied in the original meaning of the word; but it is a natural derivative from it. Reason can apprehend, when revealed, that which it cannot discover; but seldom or never can it comprehend it perfectly. In this verse the mystery is declared to be in accordance with the good pleasure of God’s will, which (it is added) He purposed in Himself. In this seems to be implied that though in some sense we can know it, yet in its fullness it passeth knowledge.