By definition, God is the highest authority possible (Heb. 6:13), so what He says is the final arbiter of truth. And if the only place we have His words is Scripture, then Scripture is the highest court of authority to which we can appeal. Nothing else is on the same level, for only Scripture is “God-breathed”, or theopneustos (2 Tim. 3:16–17).
From The Heart of the Reformation Devotional