Ephesians 3:6

What is this; "fellow-heirs, and fellow-partakers of the promise, and fellow-members of the body?" This last is the great thing, that they should be one body; this exceeding closeness of relation to Him. For that they were to be called indeed, that they knew, but that it was so great, as yet they knew not. This therefore he calls the mystery. "Of the promise." The Israelites were partakers, and the Gentiles also were fellow-partakers of the promise of God. "In Christ Jesus through the Gospel." That is, by His being sent unto them also, and by their believing; for it is not said they are fellow-heirs simply, but "through the Gospel." However, this indeed, is nothing so great, it is in fact a small thing, and it discloses to us another and greater thing, that not only men knew not this, but that neither Angels nor Archangels, nor any other created power, knew it. For it was a mystery, and was not revealed. "That ye can perceive," he saith, "my understanding." This alludes, perhaps, to what he said to them in the Acts, that he had some knowledge that the Gentiles also were called. This, he says, is his own knowledge, "the knowledge of the mystery," which he had mentioned, viz., "that Christ will in Himself make of the twain one new man." For by revelation he was instructed, both he and Peter, that they must not spurn the Gentiles; and this he states in his defence.