Muslims believe that the concept of the Trinity is not found in the Old Testament and contradicts the oneness of God.

The Old Testament contains numerous passages that hint at a complex unity within the Godhead. For instance, in Isaiah, we see references to the 'Servant of the Lord' who is both distinct from and yet one with God. This complexity is further revealed in the New Testament, where Jesus claims equality with the Father, demonstrating a relationship that transcends mere human understanding. The concept of perichoresis illustrates how the Father, Son, and Holy Spirit are distinct yet fully united in their divine essence and purpose. Furthermore, Jesus' statements about His relationship with the Father, such as 'I and the Father are one' (John 10:30), highlight the intimate fellowship and unity that exists within the Godhead. This is not a contradiction of monotheism but rather an affirmation of the depth of God's nature as revealed through scripture. The mutual indwelling of the divine persons is a foundational aspect of Christian theology that finds its roots in the Old Testament. In summary, the Christian understanding of God as a Trinity is not a departure from the oneness of God but a fuller revelation of His nature as seen in both the Old and New Testaments. The unity and diversity within the Godhead are essential to understanding the relational aspect of God's character, which is evident in the life and teachings of Jesus Christ.