Naaji at least we are now finding common ground for our discussion and that is good
So now let us address the major differences.
You mentioned that the Gospels (injil) is at least partly distorted by translation. Problem is, assuming that to be true, neither you nor I know which parts have been distorted. We need to be careful in saying that, when the Scriptures themself assert that no part of God's word wll pass away until Heaven and Earth do.. and that hasn't happened yet. (Matthew 5:17)
Now, I know that in your own faith, there are issues which the Quran does not define resolutions for, and you use your prophets' life and informal sayings as the ultimate authority on those issues. (the hadiths) Even the Shari'a the Islamic law developed out Councils held to discuss these issues (in Sunni Islam between 750AD - 850 AD) ..man's interpretations of even your holy book.
Now I am also aware than Shi'ite Islam and possibly Sufi Islam, do not agree with all the hadiths, however, doesn't it even show that despite the high place of the Quaran, you also have men speaking and telling you of it's interpretation?
The Bible asserts that all parts of the Scriptures, which Christians believe to be the Old and New Testament were written as men were carried along by the Holy Spirit. Now, however you choose to view Him (and he is definitely not Paul logic.. Paul never believed himself anything other than a Jew touched by God through a very personal encounter with Jesus on the Road to Damascus) the Holy Spirit was as much sent by God as you believe the Angel Gabriel was in coming to Muhammmad with the message of Allah.
Islam believes the Quran to be the final word of God through the prophet, Both the Bible and the Quran call Jesus Christ "The Word of God" both pointing to the eternal nature of The Word of God.
Now notice the difference.. the Quran is essentially the product of one man. It's content spans approximately 20 years and with in a single cultural context. The Bible spans about 1500 years, was written in several different languages, by several different authors and in highly divergent cultures.
Now let's look at the central message of both ... the central message of the Quran is as I understand it is to develop the theological themes of God and judgement as well as detailed instructions for life and behaviour.
The Central message in the Bible could be considered with the same themes, but there are two major differences... in the Quran the basis of judgement is a sincere submission to the Allah's will. Even sincere Christians and Jews who live by the obligations of Allah MAY enter heaven.
Islam focuses on heaven as a reward and hell as a punishment, but confession of faith to Islam is only the first step in a life that might eventually be rewarded in heaven.
Christianity and the Bible however states differently... Christians who are truly born again know they are heaven bound. Even the believers of old.. Hebrews 11 talks of the faith that "saved" the OT believers who were looking for what they hoped for but could not see" ( Hebrews 12:1) . The Jews have always believed their Messiah would come. Many Messianic Christian Jews have found that in Jesus Christ, all the prophets foretold and they were expecting has been fulfilled.
Galations 4:4 states "when the fulnesss of time had come, God sent His Son, born of a woman, born under law to redeem those under Law that we might receive the full rights as sons." Jesus Himself asserted "I have come to fulfil the Law not to abolish it ... Matthew ) and He Himself asserted it again in Luke 4:34 "Today this scripture is fulfilled in your hearing" concerning OT prophecy about His coming. (cf Isaiah 61:1-2)
For the Christian, there is the very definite knowledge that EVERY sin is forgiven, there is no longer need to try and become acceptable to God, no requirement to earn salvation by doing anything. (mind you, the true believer is so in love with God, they do it because they want to obey him, not out of the consequences of not obeying him (Romans 8.. the entire chapter)
Now.. how do we know that Jesus's death was for all people? Let's look first at Gen 12: 1-3. Abraham was told he was to be the father of many nations.. and from him came the lines of Isaac and Ishmael. But was this the father hood that God was speaking of? No, it's all true born again believers from all nations. Jesus himself says that in John 3:16... "God so loved the world" and again in Matthew 28: 18 - 20. He gave the Great Commission to His Disciples.. to go into all the world and make disciples of all nations" The word used here in the Greek is ethne meaning people groups... so it's not even enough to have a country call itself a Christian country.. even the smallest people group is loved and known by God and salvation offered to them.
Now finally in answer to your post.. even if we both agree to disagree over whether or not Jesus is God come in the flesh... to save us only as a human could have done (Galations 4:4) and if we accept what Logic says about the fact that Christians should accept Jesus's teachings and not those of the writers of the New Testament.. then it still brings us to the same conclusion... outside of Christ and His death on the cross, there is no forgiveness for sins. (Romans)