According to his page at Theopedia, “Wayne Grudem is a New Testament scholar turned theologian, author, and Research Professor of Bible and Theology at Phoenix Seminary, Arizona.” One of his best known books, from my perspective anyway, is Systematic Theology: An Introduction to Biblical Doctrine. This is a book that is worth owning, reading and studying and is widely respected and used in the Christian community at large.
Chapter 8 is titled “The Four Characteristics of Scripture: (4) Sufficiency. Is the Bible enough for knowing what God wants us to think or do?” What follows are several paragraphs from this chapter.
We can define the sufficiency of Scripture as follows: The sufficiency of Scripture means that Scripture contained all the words of God he intended his people to have at each stage of redemptive history, and that it now contains all the words of God we need for salvation, for trusting him perfectly, and for obeying him perfectly.
This definition emphasizes that it is in Scripture alone that we are to search for God’s words to us. It also reminds us that God considers what he has told us in the Bible to be enough for us, and that we should rejoice in the great revelation that he has given us and be content with it.
But the truth of the sufficiency of Scripture is of great significance for our Christian lives, for it enables us to focus our search for God’s words to us on the Bible alone and saves us from the endless task of searching through all the writings of Christians throughout history, or through all the teachings of the church, or through all the subjective feelings and impressions that come to our minds from day to day, in order to find what God requires of us.
In a footnote to that sentence he adds,
This is not meant to imply that subjective impressions of God’s will are useless or that they should be ignored. That would suggest almost a deistic view of God’s (non-)involvement in the lives of his children and a rather mechanical, impersonal view of guidance. God can and indeed does use subjective impressions of his will to remind and encourage us and often to prompt our thoughts in the right direction in many rapid decisions that we make throughout the day — and it is Scripture itself that tells us about these subjective factors in guidance (see Acts 16:6-7; Rom. 8:9, 14, 16; Gal. 5:16-18, 25). Yet these verses on the sufficiency of Scripture teach us that such subjective impressions can only remind us of moral commands that are already in Scripture, or bring to mind facts that we (in theory at least) could have known or did know otherwise; they can never add to the commands of Scripture, or replace Scripture in defining what God’s will is, or equal Scripture in authority over our lives.
Because people from all kinds of Christian traditions have made serious mistakes when they felt confident that God was “leading them” to make a particular decision, it is important to remember that, except where an explicit text of Scripture applies directly to a situation, we can never have 100 percent certainty in this life that we know what God’s will is in a situation. We can only have varying degrees of confidence in different situations. Though our ability to discern God’s will should increase as we grow in Christian maturity, we will invariably make some mistakes. In this regard, I have found helpful a sentence from Edmund Clowney: “The degree of certainty we have with regard to God’s will in a situation is directly proportional to the degree of clarity we have as to how the Word of God applies to the situation” (from a personal conversation, November 1992).