The Council of Nicaea, held in A.D. 325, was a significant ecumenical gathering of church leaders convened by Emperor Constantine to defend the deity of Christ against the heresy of Arianism. The Council affirmed that the Son is of the same substance as the Father and produced the foundational Nicene Creed to articulate this essential truth.
The Council of Nicaea was primarily convened to address the false teachings of Arius, who denied the eternal, co-equal deity of the Son. The Council affirmed that Christ is 'very God of very God; begotten of the Father, not made; of one substance with the Father' (Nicene Creed). This gathering served as a vital defense of the gospel, ensuring that the church continued to worship the true, eternal Son rather than a creature or subordinate god. As the Institutes of the Christian Religion Ch.9 §8 notes, while we do not grant councils the status of infallible oracles, we rightly reverence the Council of Nicaea because its decrees contained the 'pure and genuine interpretation of Scripture' to crush the enemies of the gospel.
Reformed theology maintains that councils are not the rule of faith; Scripture alone is the final authority. Westminster Confession of Faith Ch.31 §4 reminds us that 'all synods or councils since the apostles' times, whether general or particular, may err, and many have erred; therefore they are not to be made the rule of faith or practice.' We value Nicaea precisely because it did not invent new doctrines, but rather bore witness to what the Scriptures had always revealed about the Son of God. The Scots Confession Ch.XX clarifies that the reason for such councils was 'to refute heresies, and to give public confession of their faith to the generations following, which they did by the authority of God's written Word.'