This is the last Sunday in Advent. The epistle text from Romans holds the line concerning prophetic expectations and their fulfillment in Jesus the Messiah. Romans 16:25-27 presents for its readers both the anticipation of God’s Messiah and advent of God’s Messiah: Promises made and promises fulfilled.
To be sure, these three verses constitute a doxology, but there is rich Advent and incarnational theology to be proclaimed, too. While a doxology is usually directed toward God as worship and adoration, here Paul intends his auditors or readers to receive it too, as gospel for them. And it is indeed gospel for the subject-matter and substance of these verses consists of Jesus Christ.
The prophetic aspect may be found in the words: “...according to the revelation of the mystery kept secret for long ages” (verse 25). Something was revealed or else it would not have been known and anticipated as a “mystery.” Jesus Himself said the mystery of the incarnation can be found in “the Law of Moses and the prophets and the Psalms” (Luke 24:44). But the thing to rejoice in is the fact of its unveiling. The mystery has been revealed! The mystery, of course, is the Gospel. It is the reality that God has come to rule and reign on Earth in Jesus the Son through the power of the Holy Spirit by grace, mercy, truth, peace, and love. The mystery revealed is how this is the day of grace, that is, the day of the gracious reign of God in the power of forgiveness. Paul makes several references to this mystery and its unveiling. Christ is the mystery for Christ is the Gospel (reference Ephesians 3:9 and Colossians 1:26 as well).
This good news is multifaceted. Verse 26 underscores the scope of the Gospel in terms of its implications for the world. The Gentiles, too, have received it:
“The revelation of the mystery that was kept secret for long ages but has now been disclosed and through the prophetic writings has been made known to all nations, according to the command of the eternal God, to bring about the obedience of faith.”
The mystery revealed is how this is the day of grace, that is, the day of the gracious reign of God in the power of forgiveness.
Note the strong adversative “but,” as in but now things are very different. What was once a mystery is no longer so. The Gospel “has been disclosed” and “made known to all nations.” Here is why: It was the command of the eternal God “to bring about the obedience of faith.” God so loves the world that He sends His only begotten Son so both Jew and Gentile may be justified by faith in Jesus, which results in a new life, a new kind of obedience, the result of regeneration, not mere human effort to amass merit. This concern of God which has resulted in a command to get the Gospel out to all people is global in its scope.
Again, note the place of “the prophetic writings.” These writings were veiled until the advent of the Messiah. Now, these self-same prophetic writings, in light of the life, death, resurrection, and ascension of Jesus the Messiah, are the source of making known to all nations the command of God to bring about conversion and allegiance to Jesus through the gift of faith. Therefore, the Gospel may be found and known in the prophetic writings. Preachers would do well to couple the Old Testament lesson from 2 Samuel 7 with this text from Romans 16.
Lastly, controversies over some supposed division between Jesus and Paul are quickly laid to rest. Juan De Valdés notes:
“By saying ‘according to my gospel’ I understand Saint Paul to mean, ‘God is able to strengthen you in concord with what is preached and affirmed in the gospel that I preach.’ The expressions ‘the preaching of Jesus Christ’ and ‘my gospel’ are synonymous.”
Paul learned the Gospel from Jesus Christ Himself. What is more, although the language may be asymmetrical when compared to other Pauline doxologies, the content is the same and this text can be received with confidence as the inspired Word of God.
Concordia Theology-Various helps from Concordia Seminary in St. Louis, MO to assist you preaching Romans 16:25-27.
Text Week-A treasury of resources from various traditions to help you preach Romans 16:25-27.
Lectionary Kick-Start-Check out this fantastic podcast from Craft of Preaching.
 De Valdés, Juan. Commentary upon Romans. 292. Cited in Reformation Commentary on Scripture: New Testament Vol. VIII, Romans 9-16, edited by Philip D. W. Krey and Peter D. S. Krey. Downers Grove, IL: IVP Academic, 2016. 257.