"I believe in Jesus Christ, his only Son, our Lord. He was conceived by the power of the Holy Spirit and born of the Virgin Mary. He suffered under Pontius Pilate, was crucified, died, and was buried." - Apostles Creed
"God has no son" - Dome of the Rock in Jerusalem.
When people tell me 'all Jews, Muslims, and Christians worship the same God' I tend to cringe. The idiocy behind this claim is three-fold. First, it perceives the deity alone to be the essence of a religion. Wrong. In almost every case of religious tension it is the human authority the diety has left that causes the strife. You see this in Islam, and Christianity. All the fights are essentially over who has the right to interpret and declare orthodoxy. Second error, it is factually incorrect. Orthodox Christians are Trinitarians, or 'monothreeists' rather than 'monotheists', they admit a plurality of persons in the Godhead: Jesus Christ IS God for Christians and thus "our Lord" as the creed states. This is entirely anti-thetical to Judaism and Islam. Finally, the error only looks at the Substance of God, and not the Actions of God. It is tantamount to saying 'James and I are both humans, therefore we're the same'. While we might share a Substance (we both have Human Natures), we have almost none of the same actions or qualities which define us. Twins might be alike genetically, but what they choose to do in life, makes them separate people.
Jesus is said by Traditional Christianity to have a divine and human nature. That is, from eternity past, God the Son has existed in a loving communion with his Father and Spirit. However when he became man, he assumed a human nature, that is, he took up flesh and a human spirit, and was then completely man, and completely God. A good analogy are the children of Irish parents who were born in the United States. By their birth they are Americans, but because of their parentage, they are also granted Irish citizenship. When we misunderstand the two natures of Christ (human and divine) we come to all sorts of errors. Last night at work, a Mormon was laughing at the idea of the Trinity because in St. Matthew's gospel Jesus says that the son of man (himself) does not know the hour or the day when he will be sent back to earth. I explained that as a human person, Christ had no divine knowledge, he did not know all, and the only prophetic enlightenment he had, came from the filling of the Holy Ghost/Spirit just like any of us could receive. He didn't know how to respond then. The Church Catholic fought and defined Christ's person for some 800 years. It would be foolish to dismiss all of their work as idle talk.
Why does this matter:
To say God is unitary like post-Christian Judaism and Islam do, is to say that God is not loving. Love implies a relationship between two things. If God is one lone person outside time and space, he could not love. He existed for 'eternity past' without any other being, thus how could he be loving? On the contrary, Christianity says, that God is a loving communion within himself. He is three persons bound by one substance, as three members of a family could all share the common substance of humanity. Therefore, creation itself can be explained as an overflowing of divine love. And the apostle says himself that 'we love because he first loved us'.
Finally, Christianity counters Islam and Judaism by putting for the Lord Jesus Christ as the only way to salvation. If he were merely God, he could not act on behalf of humanity, and were he only man, he could not have had a sacrifice of infinite worth. However because Jesus was the 'God-man', he was able to offer up his life in sacrifice for the sins of the world on behalf of humanity. And as God, this offering was infinitely meritorious and on the behalf of all men. Likewise, because he was true man, he atoned for the sins of all men. This is why the fathers (condemning the errors of Calvin before he was even born) declared that Christ died for all those whose nature he assumed (that is to say, human nature). To say Christ did not die for some, would then to be saying that these people are not human.
While all of the creed is important, these article on Jesus Christ is of paramount importance, for it affirms what is unique about Christianity, condemns almost all of our current modern errors, and puts forth the only hope of the world.