Christians and Muslims both believe in the existence of the One True God. They both believe in the supremacy of this God and that He is Omnipotent, Omniscient, and Unchanging. Additionally, both religions regard God as the Creator of the universe and they believe that He is the Ultimate Judge of humanity.
However, there are striking theological differences between Christianity and Islam that can make it difficult to say that they worship the same God. Firstly, Muslims follow a strict monotheistic faith that prohibits the worship of any idols. In contrast, Christians often use physical objects such as crosses or statues to symbolize God. Christians also believe in the Holy Trinity, which is the belief in one God composed of three distinct persons: the Father, Son, and Holy Spirit. The Trinity is central to Christian beliefs and worship; it is not recognized in Islam. According to the Islamic faith, considering anyone else as divine represents the sin of (Shirk; associating others in worship with Allah), which is one of the deadliest sins in Islam.
Secondly, the fundamental beliefs of both religions differ. Christians believe that Jesus Christ is the Son of God, and he is a part of the Holy Trinity. According to Christian teachings, Jesus Christ died and was resurrected on the third day after his crucifixion. In Islam, Jesus Christ, also known as `Isa, is considered one of the prophets and messengers of God. Muslims believe that Jesus Christ did not die but was rescued and lifted alive into the heavens by Allah. Muslims also believe that Prophet Muhammad (may the peace and blessings of Allah be upon him) was the Last and Final Messenger of Allah, while Christians do not recognize Muhammad as a prophet.
Therefore, it can be argued that while Christians and Muslims hold some common beliefs, the differences in their theological beliefs and concepts of God make it difficult to claim that they worship the same God. To conclude, while both religions worship the one God, there are too many fundamental differences in their theological beliefs to establish that this God is identical.