Helpful to think this through:
In the earliest period of the Christian church, it lived by the word of the gospel proclaimed to it by the apostles, which was clarified and expanded in the Epistles and the Gospels. There was no difference between the word received in preaching and the word passed down in writing. The whole of it was based on the Old Testament, which was, at once and without resistance, accepted and recognized by the Christian churches as the Word of God. From the beginning the Old Testament was, for Christians, the book of revelation augmented and completed in these last days by the word of the gospel through the oral and written preaching of apostles. Accordingly, from the very beginning both the Old Testament and the apostolic writings held authority in the churches of Christ and were viewed as sources of knowledge. From them people drew their knowledge of God and the world, of angels and human beings, of Christ and Satan, of church and sacrament. From the most ancient times on, it was customary to demonstrate the truth of the faith, the confession of the church, by means of Holy Scripture, the Scriptures of the prophets and apostles. Dogma was that which Christ and the apostles had taught, not that which had been conceived by philosophy. Scripture was the rule of faith (regula fidei); confession and church were subordinate to it. The most ancient and, from ancient times, the most important proof for the dogma was the proof from the Scripture.
Bavinck, Reformed Dogmatics (1:61)
Bavinck goes on to talk about how tradition eventually surpassed the authority of Scriptures in the church. While the Reformation and like-minded churches have done much to recover the authority of Scripture as the rule of faith within the church, there is still much work to be done. Sola Scriptura and regula fidei are not popular talking points in a postmodern, pragmatic church age, but it would do God’s ministers well to think these things through.