Muslims might argue that the concept of God being a Trinity is not supported in the Old Testament, as it emphasizes the oneness of God.

Isaiah 6 presents a powerful vision of God, where Yahweh is seen seated on a throne, emphasizing His glory and holiness. The thrice-repeated declaration of 'Holy, holy, holy' underscores the unique nature of God, while the use of both singular ('I') and plural ('Us') pronouns suggests a multi-personal aspect to His being. This indicates that the biblical authors, including Isaiah, understood God as a uniplurality, which aligns with the Christian doctrine of the Trinity. Furthermore, other passages in Isaiah reinforce this understanding. For instance, Isaiah 48:16 mentions both the Lord God and His Spirit, indicating a cooperative relationship among divine persons. Similarly, Isaiah 61:1 speaks of the Spirit of the Lord empowering the prophet, further illustrating the multi-personal nature of God. These texts collectively point to a complex understanding of God's identity that transcends mere oneness. Additionally, other Old Testament prophets also affirm this multi-personal aspect of God. The experiences of these prophets, who encountered the Spirit of the Lord and were commissioned by God, support the notion that the Old Testament does not merely advocate for a strict monotheism devoid of plurality. Instead, it reveals a God who exists in a relational and multi-personal manner, which is foundational to the Christian understanding of the Trinity.