In the Holy Quran, the call for religious unity and the emphasis on common principles between Islam and the People of the Book (Christians) is repeatedly highlighted. This article undertakes a comparative study of the monotheistic teachings of Islam and Christianity based on verse 64 of Surah Al-Imran ("Say, O People of the Book, come to a common word between us and you"). This verse stresses the fundamental role of monotheism in fostering closer relations between religions and invites dialogue based on shared principles. The primary aim of this research is to analyze the Quranic call for monotheistic unity between Muslims and the People of the Book, especially Christians, while examining the commonalities and differences in the understanding of monotheism, polytheism, and servitude in both faiths. The research methodology adopts a comparative approach, utilizing Islamic exegesis and Christian sacred texts to analyze these concepts. The findings reveal that although both religions emphasize monotheism, significant conceptual differences, such as the Trinity in Christianity and the rejection of polytheism in Islam, are evident. The article also underscores the importance of interfaith dialogue for achieving mutual understanding and religious synergy, proposing the aforementioned verse as a foundation for such interactions.