This paper focuses especially on the pre-modern protestant understanding of Scripture as principium of theology and the role of the testimonium Spiritus Sancti in the reception of Scripture. Premodern and early modern theology shared the conviction that God's revelation is the sole starting point for all theological reasoning. Disagreements between Rome and the Reformation concerned not revelation itself, but its sources and mediation: whether theology rests on the self-authenticating authority (autopistia) of Scripture or of the Church. By contrast, modern foundationalism relocates the starting point of knowledge in the autonomous subject. I argue that contemporary theology risks conflating the premodern appeal to revelation with modern foundationalism, thereby either rationalizing Scripture defensively or relativizing its authority altogether. Against this backdrop, I revisit Calvin's account of the testimonium Spiritus Sancti as a model of integrated exegesis and doctrine. For Calvin, the Spirit's testimony is not an alternative source of revelation but the divine act by which Scripture is recognized as God's Word, illuminating the mind, sealing the heart, and grounding assurance of salvation. Scripture's authority is thus both objective (rooted in divine inspiration) and subjectively received through the Spirit—extra nos, yet inwardly effective. This premodern integration resists both subjectivism and rationalism. It shows how Scripture, doctrine, church proclamation, and pneumatology belong together in a single theological practice. I conclude by suggesting that contemporary theology can recover this integration by rethinking the relation between autopistia and testimonium, allowing Scripture to function as the living Word received and confessed within the communion of the church. Though the doctrine of Scripture is pneumatological in essence, it nevertheless should maintain a place in the prolegomena. Section II, Part 1: Before the Shift