Clarke's Bible Commentary - Ephesians 3:4
Verse 4. Whereby, when ye read] When ye refer back to them. Ye may understand my knowledge] Ye may see what God has given me to know concerning what has been hitherto a mystery - the calling of the Gentiles, and the breaking down the middle wall between them and the Jews, so as to make both one spiritual body, and on the same conditions.
John Gill's Bible Commentary
Ver. 4. Whereby when ye read , &c.] The above chapters, and seriously consider what is contained in them: ye may understand my knowledge in the mystery of Christ of his person, office, and grace; and which knowledge was very large indeed.
Matthew Henry Commentary
Verses 1-7 - For having preached the doctrine of truth, the apostle was a prisoner but a prisoner of Jesus Christ; the object of special protection an care, while thus suffering for him. All the gracious offers of the gospel, and the joyful tidings it contains, come from the rich grace of God; it is the great means by which the Spirit works grace in the soul of men. The mystery, is that secret, hidden purpose of salvatio through Christ. This was not so fully and clearly shown in the age before Christ, as unto the prophets of the New Testament. This was the great truth made known to the apostle, that God would call the Gentile to salvation by faith in Christ. An effectual working of Divine powe attends the gifts of Divine grace. As God appointed Paul to the office so he qualified him for it.
Greek Textus Receptus
προς 4314 ο 3739 δυνασθε 1410 5736 αναγινωσκοντες 314 5723 νοησαι 3539 5658 την 3588 συνεσιν 4907 μου 3450 εν 1722 τω 3588 μυστηριω 3466 του 3588 χριστου 5547
Vincent's NT Word Studies
4. Whereby (prov o). Lit., agreeably to which, namely, what he had written.Mystery of Christ. The mystery which is Christ. See on Col. i. 26; Rom. xi. 25.
Robertson's NT Word Studies
3:4 {Whereby} (pros ho). "Looking to which,"according to which." {When ye read} (anaginwskontes). this epistle will be read in public. {My understanding in the mystery of Christ} (ten sunesin mou en twi musteriwi tou cristou). My "comprehension" (sunesin, #Col 1:9; 2:2). Every sermon reveals the preacher's grasp of "the mystery of Christ." If he has no insight into Christ, he has no call to preach.