On the surface it may appear that there are no major differences between Islam and Christianity. This is because in Christianity. There are major differences between Islam and Christianity such as:
One the sacred text of Islam is the Koran. The sacred text of Christianity is the Bible both old and new testaments. Islam argues that yes Jesus was given the gospel (injil) but it has been corrupted. Hence according to Islam the bible is corrupted and it should not be relied upon for religious teaching. The Christians on the other hand when they peruse through the qurianic text and see the differences it has with the Bible; they doubt whether Muhammad received the qurian from the same source as their Bible.
Secondly the birth, life and death of Jesus Christ is a major difference. In the quarian Mary the mother of Jesus is a sister to Aaron. The death of Jesus Christ is denied that it did not happen. If he did not die his resurrection is not even mentioned. While in Christianity the birth, life and death of Jesus Christ is the central and grand subject of the entire Bible;without Jesus Christ there is no good news to world and all is lost. Jesus took the body so that He can condemn sin in the flesh by living a perfect life (John 8:44). This perfect life fitted Him to be the perfect Lamb of God to take away the sins of the world. To the Christian Jesus Christ has redeemed all including Muslims. What is needed is for one to accept this gracious gift in Jesus Christ. Without Jesus Christ Christianity loses its taste, especially atoning sacrifice. So when the quarian affirms the following.
“And because of their saying: We slew the messiah Jesus son of Mary, Allah’s messenger – They slew him not nor crucified, but it appeared so unto them; and lo! those who disagree concerning it are in doubt thereof they have no knowledge thereof save pursuit of a conjecture; they slew him not for certain: But Allah took him up unto Himself. Allah was ever mighty, wise.” surah 4:157-158.
That verse clearly knocks down the central pillar of Christianity and all is lost.
Thirdly the human nature is defined differently by Islam and Christianity. In Christianity the human nature was completely married by sin when Adam disobeyed in the garden. This necessitated a saviour and reparation of man’s nature. In Islam is born with an equal ability to do good and evil. There is no original sin. Man has the ability to be either good or bad. That is why good works is emphasized as a means of attaining heaven. There is no need of a saviour and reparation of man’s nature.
The trinity is one of the highly controversial topics in both Islam and Christianity. The quarian does not mince words as it declares that if one associates partners with Allah is an infidel. While in Christianity a triline God is served. God the father, Son and the Holy Spirit is worshipped as one God in three co-equal and co-eternal persons.
Lastly the characters of Yahweh and Allah are worlds apart. Allah gives a word in the quarian and withdraws it later. Like when Muhammad was facing stiff opposition from the Arabs in Mecca, Allah accepted Lat, mannat and Al-uzzah as gods to be worshipped with Him. Later on it is said Allah recalled that verse. Yahweh of the bible does not alter what has gone out of His mouth(psalm 89:34). As He told Adam that if you eat from this tree you will surely die. He maintained that word until He Himself came and died on the cross instead of man dying forever. He became just and yet the acquitter of the unjust. This character is not seen with Allah. How Allah dealt with Adam after the fall is different from what Yahweh did.