How should Scripture and theology function as an integrated theological practice? How was this achieved prior to their modern disciplinary separation? This paper argues that this integration rests on the specific theological conviction that Scripture is formally sufficient for the grammar and generation of theological reflection and systematization. Scripture should not be understood merely as a source of doctrinal content, but as that which governs theological reasoning. Within this framework in the pre-modern period, exegesis and systematic theology were distinct yet inseparable acts within a single theological enterprise. The argument is developed through a focused analysis of Petrus van Mastricht's Theoretico-Practica Theologia, especially Book I, chapters 1-3. Mastricht orders theology architectonically, proceeding from careful exegetical engagement with Scripture, to doctrinal demonstration, and finally to practical and devotional application. This ordering presupposes Scripture as the principium formale of theology. In this framework, theology is discovered in exegesis and articulated within borders provided by the grammar of Scripture. The paper tests this methodological claim through Mastricht's presentation of divine blessedness through his exegesis of Psalm 16:11 and 1 Timothy 1:11 and 6:15. From his exegesis, Mastricht develops presentations divine aseity, immutability, and perfection as conclusions required by Scripture's own testimony and as constitutive of divine blessedness. Recent theological work, particularly in John Webster, has drawn renewed attention to the formal role of Scripture within theological reasoning. Such retrievals suggest that the premodern integration of exegesis and doctrine may be recovered by reassessing the theological judgment concerning Scripture's place and function.