The work of the Spirit in enabling us to hear Scripture as God’s word can be seen in two parts: illumination and demonstration. First, the Holy Spirit illumines or opens our mind to behold the divine excellence that is contained in Scripture. He regenerates our noetic faculties such that we are able to hear the words of Scripture as God’s personal message to us. IN essence, the Spirit as the divine author of the text opens the text to us. Second, the Holy Spirit demonstrates or testifies to the truth of Scripture. In 1 Corinthians 2:4-14 and 1 Thessalonians 1:5, Paul attributes the persuasive and convicting power of the gospel to the testimony of the Holy Spirit. The testimony of the Spirit then provides us with the certainty that Scripture is indeed the word of God. Calvin remarks:
If we desire to provide in the best way of our consciences—that they may not be perpetually beset by the instability of doubt or vacillation, and that they may not also boggle at the smallest quibbles—we ought to seek our conviction in a higher place than human reasons, judgments, or conjectures, that is, in the secret testimony of the Spirit. (Institutes, 1.7.4.)
The certainty afforded by the Holy Spirit is not a formal certainty: it is not self-evident or incorrigible in the sense that 1+1=2. Rather, it is a moral certainty that gives one cognitive rest or peace regarding the divine authority of Scripture.
Scripture is self-authenticating: it attests to its own divinity. But we need the Spirit to illumine that self-attestation, and we need the Spirit to testify and assure us that self-authentication is valid and true. In so doing, the Spirit does not provide new evidences, but testifies to the truth that is objectively inherent in the text. The Spirit then is not the reason for faith, but the cause of faith. The reason for faith would be Scripture’s self-attestation as seen in the explicit and implicit claims of Scripture to be the word of God as mentioned earlier in this essay. The Spirit is the cause of faith because he illumines our minds and furnishes us with the assurance that the claims of Scripture are true, making us perceive and accept the authoritative status of Scripture as the word of God. This does not mean that Scripture lacks intrinsic authority before the work of the Spirit. Scripture has objective authority in and of itself, as it is the inspired word of God. The Spirit, however, works existentially within an individual and establishes the subjective authority of Scripture with respect to that individual. (Te-Ti Lau, “Knowing the Bible Is the Word of God Despite Competing Claims” in D.A. Carson, ed. The Enduring Authority of the Christian Scriptures [Grand Rapids, Mich.: Eerdmans, 2016], 989-11012, here, pp. 1007-8)