The Word of God, contained in the scriptures of the Old and New Testaments, is the final authority for our beliefs and practices. It is our unchanging “primary standard.”
Of course, lots of churches would say that, yet disagree about those beliefs and practices. A person’s understanding of what God is saying in Scripture is his creed. (Every Christian has a creed: even those who denounce creeds are making a credal statement when they do so.) And when Christians share a coherent set of beliefs with one another, and say it clearly and publicly, it’s called a confession.
The Orthodox Presbyterian Church, like its predecessor and sister denominations, uses the Westminster Confession of Faith, together with the Westminster Larger and Shorter Catechisms. These documents summarize and articulate what the Bible says on key subjects. They are our “secondary standards,” and have been altered very little since they were written in the 1640s by an international assembly of pastors, elders, and teachers at Westminster Abbey in England.
Many other creeds and confessions are faithful to Scripture and have met the needs of Christ’s people at various points in history. Some of them we still use in our teaching or worship, like the Nicene Creed, the Definition of Chalcedon, and the Heidelberg Catechism. But it’s the Westminster standards to which the OPC is formally committed, and all our church officers must accept them.
When it comes to everyday matters, the OPC uses a Book of Church Order. It contains practical rules for church government, discipline, and worship. These are our “tertiary standards.” The church modifies them every few years as we try to bring ourselves more and more in line with our primary and secondary standards: the Word of God and our shared confession of it.