Nearly forty years ago, I was a part of a group known as the International Council on Biblical Inerrancy. Concerned about the impact of liberal higher criticism, we gathered to define what it means that the Bible does not teach any error and to articulate a defensible position on the trustworthiness of God's Word that Christians could use to combat misunderstandings and misrepresentations of the church's historic position on the Bible. The council developed the Chicago Statement on Biblical Inerrancy, which deals with many issues related to the inspiration and truthfulness of Scripture. Article XVII of this statement asserts, in part, that "the Holy Spirit bears witness to the Scriptures, assuring believers of the truthfulness of God's written Word."
By this article we wanted to make it clear that the Bible is the Holy Spirit's book. He is involved not only in the inspiration of Scripture, but is also a witness to Scripture's truthfulness. This is what we call the "internal testimony" of the Holy Spirit. In other words, the Holy Spirit provides a testimony that takes place inside of us—He bears witness to our spirits that the Bible is the Word of God. Just as the Spirit bears witness with our spirits that we are children of God (Rom. 8:16), He assures us of the sacred truth of His Word.
Despite its importance, the internal testimony of the Spirit is subject to misunderstanding. One of these misunderstandings relates to how we defend the truthfulness of the Bible. Do we need to provide an apologetic—a defense—for sacred Scripture that relies on evidence from archaeology and history, on demonstrating the Bible's internal consistency, and on logical argumentation? Some misconstrue the doctrine of the internal testimony to mean that the presentation of evidence to the veracity of the Bible is unnecessary and even counterproductive. All we need to do is rest on the fact that the Holy Spirit tells us that the Bible is God's Word both in direct biblical statements and in His internal work of confirming Scripture's truthfulness.
Those who hold this position usually want to stress that the authority of God's Word depends on God Himself and believe that subjecting His Word to empirical testing is to make the Bible's truthfulness dependent on our own authority to evaluate its truth claims. At one level, this concern is laudable. Scripture's authority depends on its being the revelation of God, above whom there is no higher authority. But when we are talking about proof for the veracity of Scripture, we are not talking about the authority of God's Word but about how we know which of the books that claim to be the Word of God are actually from Him. Here, subjective experience cannot be our only court of appeal. We need some sort of objective testimony to determine whether the Bible, Qur'an, or Bhagavad Gita is the Word of God because they all claim to be the Word of God.
This is where what John Calvin called the indicia come into play. The indicia—indicators—are testable, analyzable, falsifiable, or verifiable aspects of proof. They include such things as archaeological evidence, Scripture's conformity to what we know about history from other sources, its internal consistency, its majesty and beauty, and so forth. These things give us objective confidence that the Bible is indeed the Word of God. Both Calvin and the Westminster Confession of Faith tell us that these indicators are enough in themselves to convince people that Scripture alone is the Word of God.
However, these authorities both recognize the difference between proof and persuasion, and it is really the work of persuasion that we are discussing when we look at the internal testimony of the Spirit. Human beings are adept at rejecting objective evidence when it does not confirm their prejudice, no matter how clear or compelling the evidence may be. Some people will not be persuaded by all the proof in the world because they are not truly open to the evidence.
My experience as an apologist and minister has shown me that the real reason most people reject Christianity is not for lack of evidence. The proof from external sources regarding the truth of the biblical account is too overwhelming. No, the real issue is a moral one. The person not reconciled to God in Christ and living in disobedience does not want Scripture's claim that God has a full and final claim on his life to be true. He wants to get rid of the book as fast as he can.
This is where the internal witness of the Spirit comes in. Only those whom God the Holy Spirit has regenerated will submit to Scripture as His inerrant and infallible Word. The Holy Spirit does not give us a new argument for the truth of the Bible, but He confirms in our hearts the truth of Scripture as it is displayed in both the internal marks of Scripture (harmony and majesty of its contents) and the external marks of Scripture (historical accuracy). Objective proofs for the Bible are many and compelling, but they cannot force people to believe against their wills. Sinners are only persuaded to receive the Bible as God's Word as the Holy Spirit changes their hearts and assures them that they can trust and rely on what Scripture says.