I’ll start with Judaism. Keep in mind there is much more to the beliefs of each religion, but I’ll just give a basic summary. Jews believe in the Torah, which consists of the first five books of the Old Testament of the Bible. Yes, God is the same between Christianity and Judaism in this aspect. However, Jews do not recognize the rest of the O.T., or the N.T., as the direct Word of God, as Christians do. They also do not believe Jesus Christ was the son of the God. They believe he was a prophet, but not the savior of mankind. They believe that the promised messiah has yet to come. So yes, Christians and Jews believe in the same God technically, but Jews don’t believe in the rest of what Christians believe about God that we get from the rest of the Bible. Now, that describes the Orthodox Jews. There are also Messianic Jews. And they are Jews, that do believe Jesus Christ was the son of God, and that we attain salvation through Christ.
As for God vs. Allah, that is a bit different. Let me share this article with you.
Question: “Do Christians and Muslims worship the same God?”
Answer: The Muslim and Christian views of God have many similarities. Muslims and Christians agree that there is one God who is the Creator of everything in the universe. Both view God as sovereign, omnipotent, omniscient, omnipresent, holy, just, and righteous. In these ways, the Christian and Muslim views of God are the same. However, there are also significant differences between Islam and Christianity’s view of God. While Allah (Allah is the Muslim and Arabic word for God) possesses the attributes of love, mercy, and grace, Allah does not demonstrate these attributes in the same manner, or to the same degree, as the God of Christianity.
The most important difference, though, between the Muslim and Christian view of God is the concept of the Trinity. Christians believe that God has revealed Himself as one God in three Persons: God the Father, the Son of God (Jesus), and the Holy Spirit.
God’s Son became a human being, Jesus Christ, to take away the penalty and power of sin by dying on the cross. After rising from the dead, Jesus went back to heaven to be with His Father. He sent His Spirit to teach men the truth through His Word, the Bible. One day, Christ will return to judge the earth; those who have trusted in Him will go to heaven, but those who have rejected Him must be separated in hell from the holy God.
Therefore, the belief in the Trinity is essential to the Christian faith. Without the Trinity, there is no incarnation of God in the Person of Jesus Christ. Without Jesus Christ, there is no salvation for sin. Without salvation, sin condemns all to hell. In Islam, Allah is not triune and does not have a son. Therefore, because of this key disagreement with the Christian faith, Muslims are not worshipping the God of Christianity.
So, instead of the question, “do Christians and Muslims worship the same God?” – a better question would be, “Do Christians and Muslims both have a correct understanding of who God is and what He is like?” To this, the answer is a definitive no. Because of crucial differences between the Christian and Muslim concepts of God, the two faiths cannot both be true.
Because the Bible provides the solution to sin, we believe that Christianity has the correct view of God. Becoming a human being, God’s Son died to pay for the sin of those who trust in Him. “For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life” (John 3:16).