In his Commentary on Isaiah 6.1, Eusebius assays to delineate the systematic theology of theophany. He propounds that Isaiah saw Jesus "literally," yet with spiritually enhanced vision, something that had to wait for Hezekiah's death given his burning incense in the temple (which caused the Lord's glory to depart). Eusebius draws on biblical tropes to explain why, how, when, and where Isaiah saw Jesus in Isaiah 6.1, developing en route a systematic theology of theophany. Eusebius's other works have received the lion's share of scholarly attention, and most of the little work on Eusebius's Commentary on Isaiah is quite recent, focusing on translation (Armstrong) or panorama of Eusebius's exegesis (Hollerich). Scholarship on the fine print of Eusebius's exegesis is negligible. By unfolding Eusebius's reading of Isaiah 6.1, this paper shows: 1) an early, original theological move anticipating profound influence on later understanding of theophany; 2) a spiritual-historiographical departure from Origen's reading of Isaiah's theophany; 3) an important look into Eusebius's exegetical tendencies, developing further his hermeneutic, combining theology and historiography in logical concert. This paper, among the first examinations of specific passages in Eusebius's Commentary on Isaiah, thus develops a monumental trope in nascent Christian theology, demonstrates complex interaction between Eusebius and his exegetical influences, and takes important first steps toward painting a fuller picture of the exegesis of early Christianity's great historian. Furthermore, this may constitute a precursor to Eusebius's "constitutive approach" to the Son-as-image-of-God question, which Delcogliano argues occurred around the time of this commentary's publication.