Roshd Islamic Shia Website : Ocassion Letters 2008/12/25
The Birthday of Prophet Jesus (PBUH) : Quran and New Testament 
In the Name of Allah, the Beneficent, the Merciful
Quran and New Testament
The Holy Quran clearly states that Jesus (PBUH) was a messenger of Allah (SWT) and the Gospel is a holy book just like Torah, Psalms and the Holy Quran itself. Allah (SWT) asks Muslims to believe in the Holy Books which were revealed to Moses, David, Jesus and all other prophets (PBUT).
Without any doubt, the Gospel is considered a divine book in many verses of the Holy Quran and acceptance of its validity is a condition to have faith for all Muslims. Hence, Muslims have a considerable respect and holiness for Torah and Gospel; even in some prayers we notice swearing to these two books (1).
The Holy Quran describes the Gospel in one of its verses in this manner,
And in their footsteps, we sent Isa/Jesus the son of Maryam/Mary, confirming Torah that had come before him, and We gave him the Gospel: therein was guidance, light, and confirmation of the Torah that had come before it: a guidance and an admonition to those who fear Allah.(2) One can clearly see that the Holy Quran recognizes Gospel as holder of guidance, light and advise for the pious.
However, the history of Christianity shows that Christians do not believe in a unique Gospel in which every word of it was the word of God.(3) There are four Gospels accepted by most Christians which comprise the New Testament. So, this question has always been asked that which Gospel is addressed in the Holy Quran.
The reality is that Christians believe the four Gospels were written works of man, nevertheless they consider divine value for them. Furthermore they believe the New Testament was written after the departure of Jesus (PBUH) in order to declare his Prophetic mission. (4)
Therefore contrary to the Holy Quran’s statements, a Christian does not assume that Jesus (PBUH) in fact did have a book. It is also noteworthy to mention that the Gospels do not contain even a sentence that is attributed to revelation. However, Christians claim that the Gospels have been divinely inspired, but they do not have any proof for their claim. (5)
The 4 Gospels that are considered authentic Gospels are actually 4 of the many gospels that had been in use during the first two centuries after Christ among the Christians. In the present day churches, especially Catholic churches, do not admire of talking about the many gospels that was available during the second century. However some of the gospels have made slight references to the presence of these numerous gospels. (6)
Although there are handwritten versions of the New Testament that dates back 1600 years in famous and significant libraries and museums around the world, we cannot be sure that the Holy Quran’s reference to the bible is to which book. Because just as mentioned, there is considerable difference between the Bible that Muslims believe in and that which Christians believe in.     
Muslims believe that during the lifetime of Prophet Muhammad (PBUH&HP), there were pious Christian scholars that held an original version of the Bible, which the arguments of the Holy Quran was based on that. (7) There we find in the Holy Quran and other Islamic sources that Christians have been called to believe and act upon the sayings of the Bible. The Holy Quran has also repeatedly referred to the Old and New Testament available with the Jews and Christians when debating or explaining Monotheistic religions. 
Based on monotheistic teachings the Divine Holy Books should not differ from each other because they come from one source. Therefore, Muslims believe that the reason there is a difference between the Holy Quran and the Bible is because the Gospels have changed over time.
(Selection taken from “Islam, the Chosen Religion” by Ali Reza Masjid Jame’i)
 
Roshd Website congratulates all, especially you dear friend on the birth of the chosen Servant and great Prophet of God, Prophet Isa the son of Maryam (PBUT).
 
Footnotes:
1. For example in the prayer of the night of Arafah which is taught by Imam Sadiq (PBUH), we ask our request from Allah (SWT) by swearing to the validity of Torah of Musa (PBUH) and Gospel of Isa (PBUH) and Quran of Muhammad (PBUH&HP). (Mafatih al-Jinan the chapter about acts of the night of Arafah)
2. The Holy Quran, (5:46). There are other descriptions in the Holy Quran about Gospel, for example you might refer to (3:3-4) and (57:27).
3. For example Philistian Challet the great French scholar says,” Anyway these Gospels are manmade and one cannot consider them the words of God.” (The Brief History of Great Religions, Foundations of Christianity by Karl Kautsky)
4. This means that in Islam the Prophet is the clarifier of the Holy Quran, but in Christianity the Gospels are the clarifiers of Jesus (PBUH). (Introduction to Great Religions)
5. Christian Theology by Thomas Michael
6. For example Paul forbids Galatians from accepting Gospels which are not in accordance with his teachings and says, “I wonder you turn from the one who calls you to the mercy of Jesus to other Gospels. One who brings another Gospel which you have accepted, he shall be cursed.” (Galatian, 1:6-9)
7. The Great Islamic Encyclopedia, vol. 10, description of Gospel