All Scripture is God-breathed, because the Holy Spirit superintended the biblical authors as they composed their writings, the Word of God.1Adapted from Gregg R. Allison, 50 Core Truths of the Christian Faith: A Guide to Understanding and Teaching Theology (Grand Rapids, MI: Baker Books, 20180, ch. 1.
Inspiration is a divine action that creates an identity between a human word and a divine word.John Frame
Or more fully expressed: “Inspiration is that extraordinary, supernatural influence (or, passively, the result of it,) exerted by the Holy Ghost on the writers of our Sacred Books, by which their words were rendered also the words of God, and, therefore, perfectly infallible” (B. B. Warfield).
The “word of God”
The earliest note about the word of God would be those we find throughout the Old Testament. They begin with his decrees of creation (e.g., Gen 1:3, 24) and providence (Heb 1:3), and they continue with his words of personal address (e.g., Gen 2:16-17; Exod 20:1-3; Matt 3:17). About a 100 times, we read the expression, “The word of the the LORD came to…” (וַיְהִי דְבַר יְהוָה אֵלָיו לֵאמֹר/wayhi devar yehwah elaiw lemor), and around 300 times the prophets preface their message with “Thus saith the LORD” (כֹּה אָמַר יְהוָה/koh amar YHWH). This was all fulfillment God’s promise to speak through human lips as a mode of self-revelation (Deut 18:18-20), which practiced throughout the Old Testament (Exod 4:12; Num 22:38; Deut 18:20–22; 1 Sam 15:3, 18, 23; 2 Chr 25:15–16; Isa 30:12–14; Jer 1:9; 6:10–12; 36:29–31; Ezek 13:1–7).
Of course, the preeminent manifestation of the “word of God” comes as a Person: Jesus Christ the Λόγος/Logos made flesh and now glorified.
And of course, these words spoken by God form the Bible (Deut 31:12–13, 24–26; Josh 24:26; Isa 30:8; Jer 30:2; 36:2–4, 27–31; 51:60; 1 Cor 14:37; 2 Pet 3:2)