John Gill's Bible Commentary Ver. 3. How that by revelation he made known unto me the mystery , &c.] Or is made known unto me: so the Alexandrian copy, and some others, and the Vulgate Latin version. The Gospel, which is sometimes called a mystery, the mystery of the Gospel, the mystery of godliness, and the mystery of faith: the several doctrines of the Gospel are the mysteries of the kingdom of heaven; such as a trinity of persons in the Godhead, the union of the two natures in Christ, the saints' union to Christ, and communion with him, the resurrection of the dead, and the change of living saints, and the whole doctrine of salvation by Christ, of justification by his righteousness, pardon by his blood, and atonement by his sacrifice; and this was made known to the apostle, not in a mere notional and speculative way, but in a spiritual and saving manner; not by men, for he was not taught by men, nor did he receive it from them, but had it by the revelation of Jesus Christ, and by the spirit of wisdom and revelation in the knowledge of him: as I wrote afore in few words : in the two first chapters of this epistle, which are a compendium of the mystery of the Gospel, in its several parts; as predestination, election, redemption, regeneration, and salvation by free grace.
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
οτι 3754 CONJ κατα 2596 PREP αποκαλυψιν 602 N-ASF εγνωρισεν 1107 5656 V-AAI-3S μοι 3427 P-1DS το 3588 T-ASN μυστηριον 3466 N-ASN καθως 2531 ADV προεγραψα 4270 5656 V-AAI-1S εν 1722 PREP ολιγω 3641 A-DSM
Robertson's NT Word Studies
3:3 {By revelation} (kata apokaluyin). Not essentially different from di' apokaluyews (#Gal 1:12). this was Paul's qualification for preaching "the mystery" (to musterion. See #1:9). {As I wrote afore} (kaqws proegraya). First aorist active indicative of prografw as in #Ro 15:4, not picture forth as #Ga 3:1. But when and where? Epistolary aorist for this epistle? That is possible. A previous and lost epistle as in #1Co 5:9? That also is abstractly possible. To the preceding discussion of the Gentiles? Possible and also probable. {In few words} (en oligwi). Not = pro oligou, shortly before, but as in #Ac 26:28 "in brief space or time" = suntonws (#Ac 24:4), "briefly."