canon
Grudem's approach seems to suggest a binary scale: all of God's/godly communication outside of the canon is meaningless, all inside the canon is of the same value. This doesn't reflect progressive revelation and orders of relevance within the canon, nor the blurring at the fringes of canon (deuterocanonical books).
Systematic Theology: An Introduction to Bible Doctrine
If we are to trust and obey God absolutely we must have a collection of words that we are certain are God’s own words to us