Rom 16:25-27 Now to Him who is able to establish you according to my gospel and the preaching of Jesus Christ, according to the revelation of the mystery kept secret since the world began but now has been made manifest, and by the prophetic Scriptures has been made known to all nations, according to the commandment of the everlasting God, for obedience to the faith---- to God, alone wise, be glory through Jesus Christ forever. Amen.
To be noted here is that it is God's command for the gospel to be made known to all nations. Those who are not involved in promoting and propagating the gospel are not obeying God's command. But that should not even be an issue for those who believe the gospel. For if we believe the gospel, we will speak it. It is written: "I believed; therefore I have spoken." With that same spirit of faith we also believe and therefore speak. 2Cor 4:13 For we realize that "since we know what it is to fear the Lord, we try to persuade men." 2Cor 5:11, given that apart from faith in the gospel there is no promise for salvation from God's wrath, "the mystery which has been hidden from ages and from generations, but now has been revealed to His saints." Col 1:26
What is it to be "established" but to be made strong in conviction, unshakeable in faith, which is part of the sanctification process, which itself is part of the salvation package, as Paul indicates here saying, "according to my gospel and the preaching of Jesus Christ." For "the Lord is faithful, who will establish you and guard you from the evil one." 2Th 3:3 That's part of the gospel message. The gospel is not just about justification. It's also about the security we have in Christ, the empowering by the Holy Spirit, and the effect regeneration has on our behavior.