The biblical canon was not determined by the decree of an earthly church, but by the inherent divine authority of the Scriptures themselves, which the Church recognized over time through the inward testimony of the Holy Spirit. While the Church received and testified to these books, its role was to acknowledge the authority God had already placed within them rather than to confer that authority.
The authority of the Holy Scriptures is derived not from the judgment or approval of the Church, but directly from God, who spoke through the prophets and apostles. As stated in the Belgic Confession Art. 5, we receive the canonical books not because the Church approves them, but because the Holy Spirit witnesses in our hearts that they are from God. This internal testimony is essential, as John Calvin argues in his Institutes of the Christian Religion, because a faith resting merely on human decision would be tossed about in uncertainty. The Scripture bears its own divine majesty, and the Church, in receiving the canon, is simply acknowledging what God has already stamped as His own Word.
The Reformed tradition emphasizes that the Church discovered and recognized the canon rather than inventing it. Early councils served to confirm what was already held as the unanimous faith of the people of God, rejecting books that lacked divine inspiration. The 1689 LBCF Ch.1 §3 clarifies that the Apocrypha, not being divinely inspired, carries no authority for the Church of God. The Formula of Concord maintains that the prophetic and apostolic Scriptures are the sole rule and standard, and that all other writings—even those of church fathers—are merely witnesses to how the pure doctrine was preserved and understood throughout history.