From Christianity Today, this extract using the ancient Apostles’ Creed as the basis for understanding how and why God is not the god worshiped by Muslims:
From How can we engage in conversation and still stick to our theological guns? I propose employing the Apostles’ Creed—a time-tested and easily digestible template of basic Christianity—to remind ourselves how much our beliefs differ from Muslims’.
• I believe in God, the Father almighty, creator of heaven and earth.
While Muslims and Christians both ascribe omnipotence to the Creator, only in Christianity is he revealed as Father. “Christians,” Timothy George has noted, “predicate something essential and irreducible about God that no Muslim can accept: We call him our heavenly Father.”
• I believe in Jesus Christ, his only Son, our Lord, who was conceived by the Holy Spirit, born of the Virgin Mary …
Although our Muslim friends revere Jesus (calling him Isa) and believe he was born of a virgin and is coming again, they deny his divinity, saying he is one of many prophets. But Christians see him as the second person of the Godhead, in a community of love from all eternity with the Father and the Holy Spirit. This is not just a theological disagreement. The deity of Christ is the sine qua non of Christian theology and mission. There is no salvation if Christ is not truly God and truly man. “No one who denies the Son has the Father,” the disciple whom Jesus loved stated categorically. “Whoever acknowledges the Son has the Father also.”
• … suffered under Pontius Pilate, was crucified, died, and was buried; he descended to the dead.
Most Muslims believe Jesus only appeared to die on the cross. They reason that God would never allow his prophet to suffer such ignominy. But Christianity holds that Christ’s crucifixion, which is foolishness to Jew, Greek, and Muslim, atones for sin and offers peace with God. “And being found in appearance as a man,” Paul said, “he humbled himself and became obedient to death, even death on a cross!”
• On the third day he rose again; he ascended into heaven, he is seated at the right hand of the Father, and he will come to judge the living and the dead.
Muslims deny the Resurrection and certainly don’t believe that Isa can stand in God’s place as judge. But Christians do, affirming Paul’s confession that “every knee should bow” to Jesus, “the name that is above every name.”
• I believe in the Holy Spirit, the holy catholic Church, the communion of saints …
Muslims also believe the Holy Spirit supported the ministry of Isa, but, being strict unitarians, they deny the Spirit’s deity.
• … the forgiveness of sins, the resurrection of the body, and the life everlasting.
Muslims have no assurance of salvation.
In simplest terms, Allah is not God. By denying Christ (as distinct from the historical person of Jesus) Muslims deny the one true path to salvation.