|The Sacrifice of Isaac. (According to Islamic tradition, it was Ishmael who was nearly sacrificed)
There are similarities between the two religions, of course. Both are monotheistic: they both believe that there is only one God Who is the Maker of heaven and earth. But what makes Christianity unique and distinctive is its belief in a Savior – a divine-human being who came into the world and died on a cross to save us from our sins. This notion Islam utterly rejects.
"O People of the Book! / Commit no excesses / In your religion: nor say / Of Allah aught but the truth. / The Messiah Jesus son of Mary, / And a Spirit proceeding / From Him: so believe / In Allah and His Messengers. / Say not 'Trinity': desist" (Quran 4:171). To a devout Muslim to say that God is three-in-one is thinly disguised polytheism, and is blasphemy.
Does it make a difference? Yes! For a Christian the idea of a Savior is crucial.
Both Christianity and Islam believe that God is the sovereign Ruler of the universe and is just. Both religions teach that there will be a Last Judgment in which God will reward good and punish evil. But what Islam fails to reckon with is the extent and depth of human depravity. It is, of course, obvious that the world is full of evil – everything from marital spats to world wars. We are confronted with dishonesty and discord on a daily basis. But what is the cause of all this dysfunction? The Bible offers a striking diagnosis: the root problem is human nature. "The heart is deceitful above all things, / And desperately wicked; / Who can know it?" (Jer. 17:9; NKJV). And then the prophet adds this terrifying prospect: "I, the Lord, search the heart, / I test the mind, / Even to give every man according to his ways, / According to the fruit of his doings" (v. 10). What makes the judgment of God different from that of a human court is that God is able to examine our inward motives. And no matter what pretense we can maintain before our fellow human beings, God knows the real truth about who we are, and how we think and feel.
That being the case, how will any of us escape divine scrutiny? How will any withstand God's judgment? For the plain fact of the matter is that we are all guilty in His sight. "The Lord looks down from heaven upon the children of men, / To see if there are any who understand, who seek God. / They have all turned aside, / They have together become corrupt; / There is none who does good, / No, not one" (Ps. 14:2,3).
It is at this point that the Bible proposes a unique solution to the problem. "For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life" (John 3:16). Jesus claimed to be more than just a prophet; He is the Son of God and Savior of mankind. Coexisting eternally with the Father, He came into the world by being born of a virgin, died upon the cross as an atonement for our sin, and then rose from the dead and ascended back into heaven, where He sits at the right hand of God the Father making intercession for us. Because Christ alone is qualified to be the Savior, there is no salvation apart from Him.
Islam, then, leaves us in a hopeless position. It acknowledges the fact that God is just and will judge the world, but leaves us with no means of atoning for our sins and reconciling us to God. It's only answer to our innate lack of righteousness is "try harder." But if we are at all honest with ourselves, and measure ourselves by God's standards, we are left with the certain prospect of damnation. This is why Christianity, and only Christianity, can meet the need of mankind. Islam is a non-solution to the problem.