Considering all the various points within Romans within which you read ideas foreign to the flow of the various passages, heir, I am not surprised you do likewise where Romans 16:26 is concerned.
Romans 16:25 Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began, 16:26 But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith: 16:27 To God only wise, be glory through Jesus Christ for ever. Amen.
In contrast to verse 56 of...
Matthew 26:53 Thinkest thou that I cannot now pray to my Father, and he shall presently give me more than twelve legions of angels? 26:54 But how then shall the scriptures be fulfilled, that thus it must be? 26:55 In that same hour said Jesus to the multitudes, Are ye come out as against a thief with swords and staves for to take me? I sat daily with you teaching in the temple, and ye laid no hold on me. 26:56 But all this was done, that the scriptures of the prophets might be fulfilled. Then all the disciples forsook him, and fled.
In Romans 16:25's "the scriptures of the prophets" the word "scriptures" is the word "graphe."
While its' word "prophets" is the word "propheticos."
Whereas in Matthew 26: 56's "the scriptures of the prophets" though the word "scriptures" is the same word "graphe" its' word "prophets" is the word "prophetes."
In Mathew 26 both graphe and prophetes are plural nouns.
The scriptures; the prophets - the sense is the various scriptures of the various prophets.
Whereas in Romans 16, only graphe is a plural noun, whereas propheticos is singular as it is an adjective, and adjectives are always singular.
The sense is prophetic writings.
Paul is asserting that his "my gospel, and (the word "Kai" or even, or, that is to say) the preaching of Jesus Christ according to (or line with) the revelation of the mystery (what mystery - that) which was kept secret since the world began, but now is made manifest, and by prophetic writings, according to the commandment of - notice - the everlasting God (Aionios, in other words, God in eternity) made known to all nations for the obedience of faith: to God only wise (Sophos, or only He knew this) be glory through Jesus Christ (how - via this mystery He is working out in Him) for ever (Aion, or throughout the ages). Amen (Amen, or, only He - God was able to keep this secret).
Paul is referring to his writings about this Mystery. He is asserting that they are prophetic, or God's words through Paul.
He is basically reasserting what he began Romans with...his assertion...
Romans 1:1 Paul, a servant of Jesus Christ, called to be an apostle, separated unto the gospel of God,
1:5 By whom we have received grace and apostleship, for obedience to the faith among all nations, for his name:
Romans 15:15 Nevertheless, brethren, I have written the more boldly unto you in some sort, as putting you in mind, because of the grace that is given to me of God, 15:16 That I should be the minister of Jesus Christ to the Gentiles, ministering the gospel of God, that the offering up of the Gentiles might be acceptable, being sanctified by the Holy Ghost. 15:17 I have therefore whereof I may glory through Jesus Christ in those things which pertain to God. 15:18 For I will not dare to speak of any of those things which Christ hath not wrought by me, to make the Gentiles obedient, by word and deed, 15:19 Through mighty signs and wonders, by the power of the Spirit of God; so that from Jerusalem, and round about unto Illyricum, I have fully preached the gospel of Christ.
The gospel of God is the gospel of Christ that Paul is referring to in his Eternal God commanded and therefore, prophetic writings, as "my gospel, and the preaching of Jesus Christ according to the revelation of the mystery, which was kept secret since the world began, but now is made manifest" etc.
This here...
Romans 15:15 Nevertheless, brethren, I have written the more boldly unto you in some sort, as putting you in mind, because of the grace that is given to me of God, 15:16 That I should be the minister of Jesus Christ to the Gentiles, ministering the gospel of God, that the offering up of the Gentiles might be acceptable, being sanctified by the Holy Ghost. 15:17 I have therefore whereof I may glory through Jesus Christ in those things which pertain to God. 15:18 For I will not dare to speak of any of those things which Christ hath not wrought by me, to make the Gentiles obedient, by word and deed, 15:19 Through mighty signs and wonders, by the power of the Spirit of God; so that from Jerusalem, and round about unto Illyricum, I have fully preached the gospel of Christ.
Is this here...
Ephesians 3:1 For this cause I Paul, the prisoner of Jesus Christ for you Gentiles, 3:2 If ye have heard of the dispensation of the grace of God which is given me to you-ward: 3:3 How that by revelation he made known unto me the mystery; (as I wrote afore in few words, 3:4 Whereby, when ye read, ye may understand my knowledge in the mystery of Christ) 3:5 Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit; 3:6 That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel: 3:7 Whereof I was made a minister, according to the gift of the grace of God given unto me by the effectual working of his power. 3:8 Unto me, who am less than the least of all saints, is this grace given, that I should preach among the Gentiles the unsearchable riches of Christ; 3:9 And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ: 3:10 To the intent that now unto the principalities and powers in heavenly places might be known by the church the manifold wisdom of God, 3:11 According to the eternal purpose which he purposed in Christ Jesus our Lord: 3:12 In whom we have boldness and access with confidence by the faith of him.
He also mentioned THAT access here...
Romans 8:15 For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. 8:16 The Spirit itself beareth witness with our spirit, that we are the children of God: 8:17 And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.
8:29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
Which continues on in this here...
Ephesians 2:7 That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus.
Romans 8:18 For I reckon that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us.
Ephesians is Romans 102.