Christianity is a man-made and man-interpreted religion. Never did God authorize the formation of Christianity. Never did you hear the personality of Jesus utter to his disciples that you are Christians of Christianity, nor did you hear any of the Hebrew prophets say to the Israelites and to the Jews that their religion is Judaism. These religions are formed by later generations of man who seeked to interpret the prophets and scriptures.
No individual that the Quran claims is a prophet or messenger of God gave foundation to a religion that exists. Rather all prophets and believers since the beginning followed a universal principle. This universal principle was complete and total submission to the will of God. People are thrown off by Arabic words and think of Islam and Muslim as labels. Such a thinking is not the teaching of the Quran nor of the prophet Mohammed. Islam is not a religion, nor was Islam founded by the Arab Prophet 1400 years ago. Submission to God - Arabic word Islam - is infact a principle or 'deen' that is required by the will of God. Never does God in the Quran call Islam a religion (Arabic word Madhab), but specifically labels it as a 'way' - Arabic word 'deen' - which is to be practiced. Thus, Abraham, Moses, Jesus and Mohammed were all Muslims - Those who surrender themselves or submit themselves. We can thus conclude that this principle or way existed alongside creation with Adam and Eve, throughout the generations of man and always has been the purpose of God's creation. Any Jew or Christian will agree that mankinds purpose is to worship God, and what better way of worship then to submit to His will? God gave us commandments to follow, and by following these commandments not only are we submitting to God but showing our sincerity and faith in the existance of God. Christians will agree that no work is accepted unless it comes through faith. Muslims agree that the works we do prove our sincerity and faith because we don't have to do them, but choose to.
When one claims to believe in the existance of God, automatically that claim and that belief should lead one in the direction which God has ordained. One must practice God's commandments, otherwise there exists no real faith. Can you honestly say that you have true faith in God and yet you fail to act in accordance to His will? Now no one is perfect, and perfection is not what God seeks. God seeks that we do His will and if we fail, our faith in Him and His mercy lead us to repentance and effort to literally better ourselves. Salvation is acquired when one accepts God and His mercy as our savior. No symbolic event can save us (ie. crucifixtion), its what we do in our life to prove our sincerity and faith to God.
The Quran poses as significant question which proves the point I have made. God says in the Glorious Quran:
'Do you say that Abraham, and Ishmael, and Isaac, and Jacob and his children were Jews or Christians?' Nay, do you know better than Allah? (2:140)
This poses a significant issue. We know that Judaism and Christianity were formed several years after Abraham, Isaac and Jacob, and infact through their descendants it was Moses who was revealed the law for Israel - the Torah. So what religion or law or concept did Abraham, Isaac and Jacob follow? They could not have been Jews or Christians. The Quran explains what their "religion" was:
The same did Abraham enjoin upon his sons, - and Jacob also - saying, 'O my sons, truly Allah has chosen this religion/way/principle for you; so let not death overtake you except when you are in a state of total islam (submission).' (2:132)
O people of the Book (Jews and Christians)! Why do you dispute about Abraham, while the Torah and the Gospel were not revealed till after him? Have you then no sense? Abraham was neither a Jew nor a Christian, but he was a true Muslim and he joined none in worship with Allah (3:65-67)
We can see in the light of these verses that Abraham was among those who submitted (al-muslimoon) and did not belong to any man-made religion. We know that the terms "Judaism and Christiantiy" are not found in Biblical inscriptions, thus they must have been incorporated by later generations of man.