No doctrine is more fundamental to Reformation theology than the doctrine of God. Indeed, the distinctive emphases of the Reformation and all those who follow in the footsteps of the Protestant Reformers are fueled by the biblical, Reformed understanding of who God is. To know biblical doctrine in all its particulars, we must first know the doctrine of God. So we begin our study of Reformation theology by looking at one of Scripture’s most fundamental truths about God, namely, that there is only one God.
From the very beginning, Christianity has stood firmly upon the foundation of monotheism. Every part of Scripture, implicitly or explicitly, affirms that there is only one God, and belief in only one creator God is shared by many other non-Christian religions as well. As we will see, the monotheism taught by all Christian theological traditions, including Reformed theology, is different from the monotheism of religions such as Judaism and Islam because Christian monotheism is Trinitarian monotheism. Nevertheless, our doctrine of the Trinity is grounded in two major truths, one of which is that there is but one eternal God who has created our universe.
Today’s passage is one of many places that affirm this truth. Isaiah 45:5 firmly insists that the God revealed in Scripture is the only God. Note that when we speak of biblical monotheism, we are not speaking of deity in some generic sense. We are not talking about a vague concept of God that we arrive at via philosophical speculation, even though philosophy assists us in studying the doctrine of God. Instead, biblical monotheism proclaims that the only God is the One who redeemed Israel from Egyptian slavery and delivered His law through Moses. In Isaiah 45:5, two different Hebrew words for God appear. First, we have the word elohim, which is often used as a generic term for deity and is translated in our text as “God.” Isaiah 45:5 also features the specific covenant name of the God of Israel—Yahweh—which is rendered in English as “LORD.” Thus, we could paraphrase today’s passage as “I, the LORD of Israel, am the only deity.”
Yahweh is the only God regardless of whether we acknowledge Him as such. The addressee of Isaiah 45:5 is Cyrus of Persia (see vv. 1–4). Cyrus did not know God as He revealed Himself, specifically, as the only true God. Yet, that is irrelevant with respect to who God was in relation to Cyrus. Though Cyrus did not acknowledge Yahweh as such, He was Cyrus’ God because Yahweh alone is God.