The So-Called "Abrahamic" Religions
There is a common belief that Judaism, Christianity and Islam share a religious tradition, going back to the Biblical patriarch Abraham.
Christianity did in fact arise from first century Judaism. It was begun by a Jew whom we call Jesus and another Jew we call Paul had significant input into its evolution. It has a certain relationship to the Torah of the Jews that is known in Christianity as The Old Testament but the Jews did not and do not accept Jesus as the Messiah and certainly not as the Son of God. Abraham is a mythic figure, not an historical person, but there is a definite connection between today's Judaism and Christianity and the Judaism of the time of Jesus. In fact the name of the Judaic/Christian god is YHWH and the name of the Muslim god is Allah so they can hardly be the same.
There is no god except Allah - Quran (3:62) I am Allah: There is no god but I - Quran (20:14)
And God said unto Moses, I AM That I AM: and he said, Thus shalt thou say unto the children of Israel, I AM (yod he vav he - YHWH) hath sent me unto you - Exodus 3:13–14
Islam was created 600 years after the time of Jesus in Arabia by an illiterate trader known to us as Muhammad. He knew some stories from Jewish and Christian sources but had a very imperfect understanding of both religions. He took the Jewish concept of "prophets" sent by God to give a message to human beings and altered it to suit his arrogant claims to a unique status. These prophets included Jesus but were mainly Old Testament figures such as Adam, Abraham and Moses and some he just made-up. According to Islam these Biblical figures were all actually Muslims and the religion they taught was Islam. This was a piss poor attempt to assume the authority of Judaism and Christianity for himself and Islam. These prior prophets were pretty hopeless because the proto-Qurans kept getting lost and the message kept getting fucked up, well at least according to Muhammad. Somehow the Gospel writers forgot to mention that Jesus and his disciples called themselves Muslims:
Then when Isa (Jesus) came to know of their disbelief, he said: "Who will be my helpers in Allah's cause? Al-Hawariyyun said: "We are the helpers of Allah; we believe in Allah, and bear witness that we are Muslims. Our Lord! We believe in what You have sent down, and we follow the Messenger (Jesus); so write us down among those who bear witness. Quran (Al-Imran, 52-53)
Finally Muhammad, himself, was born to reveal the only true religion once and for all: Islam, submission to God whose name is 'Allah.' No changes to this religion and no new religions were to be allowed ever after … or else.
Muhammad was revealed the details of this religion in a series of "revelations" by the angel Jibreel that were finally collected into a book called by us the Quran. The "revelations" were not recorded as one text and this was initially done when Abu Bakr was caliph and a final recension occurred in the reign of Uthman. It is terrible in its message and opaque in its clarity. Muhammad claimed Islam superseded Judaism and Christianity but that he respected the religions and their believers. However, you'd certainly find that hard to believe after reading the Quran and studying Islam and seeing exactly how Muhammad and Muslims in power treated the Jews, Christians and other non-Muslims for the next almost 1200 years. Muslims are so arrogant that they believe everyone is born a Muslim and that parents from other cultures lead children from the true religion:
When your Lord asked all the offspring of Adam (before their birth), "Am I not your Lord?" All of them testified and bore witness to their testimony that on the Day of Judgment they would not say, "We were not aware of this (fact)" (Quran 7:172-173)
Many Christians and Jews think we should all just get together in a three-way happy family of religions ignoring the glaring discrepancies and no doubt there are Muslims who agree with them despite the reality of their differences. You can't enjoy a real open and honest relationship with a religion that actually treats yours with contempt. Allah "revealed" to Muhammad that the real religion of Abraham, Moses, David, John the Baptist, Jesus, etc was the exact same Islam that he taught and that all the great Biblical figures brought a book from Allah with them. These have all been destroyed leaving only deliberately corrupted and falsified Jewish and Christian scriptures. Because of this corruption it is forbidden for Muslims to study the Torah or the New Testament. That's right, according to Islam, the Jewish and Christian scriptures are not just bullshit, they're deliberate frauds.
Mohsin Khan: Verily, those who disbelieve [by concealing the truth about Prophet Muhammad (S.A.W.) and his message of true Islamic Monotheism written with them in the Taurat (Torah) and the Injeel (Gospel)] and prevent (mankind) from the Path of Allah (Islamic Monotheism), they have certainly strayed far away. (Quran 4:167) (Tafsir Al-Qurtubi) (See also Quran 7:157)
The Quran rejects and repudiates the definitive beliefs of the Christian religion.
The Trinity and that Jesus is the Son of God
O followers of the Book! do not exceed the limits in your religion, and do not speak (lies) against Allah, but (speak) the truth; the Messiah, Isa son of Marium is only an apostle of Allah and His Word which He communicated to Marium and a spirit from Him; believe therefore in Allah and His apostles, and say not, Three. Desist, it is better for you; Allah is only one God; far be It from His glory that He should have a son, whatever is in the heavens and whatever is in the earth is His, and Allah is sufficient for a Protector. Quran (4:171)
Jesus is the Son of God
Allah is only one God; far be It from His glory that He should have a son, whatever is in the heavens and whatever is in the earth is His, and Allah is sufficient for a Protector. Quran (4:171)
Wonderful Originator of the heavens and the earth! How could He have a son when He has no consort, and He (Himself) created everything, and He is the Knower of all things. Quran (6:101)
And the Jews say: Uzair is the son of Allah; and the Christians say: The Messiah is the son of Allah; these are the words of their mouths; they imitate the saying of those who disbelieved before; may Allah destroy them; how they are turned away! Quran (9:30)
They say: Allah has taken a son (to Himself)! Glory be to Him: He is the Self-sufficient: His is what is in the heavens and what is in the earth; you have no authority for this; do you say against Allah what you do not know? Quran (10:68)
And say: (All) praise is due to Allah, Who has not taken a son and Who has not a partner in the kingdom, and Who has not a helper to save Him from disgrace; and proclaim His greatness magnifying (Him). Quran (17:111)
And warn those who say: Allah has taken a son. Quran (18:4)
It beseems not Allah that He should take to Himself a son, glory to be Him; when He has decreed a matter He only says to it "Be," and it is. Quran (19:35)
And they say: The Beneficent God has taken (to Himself) a son. (91) That they ascribe a son to the Beneficent God. (92) And it is not worthy of the Beneficent God that He should take (to Himself) a son. Quran (19:88)
And they say: The Beneficent God has taken to Himself a son. Glory be to Him. Nay! they are honored servants Quran (21:26)
Never did Allah take to Himself a son, and never was there with him any (other) god-- in that case would each god have certainly taken away what he created, and some of them would certainly have overpowered others; glory be to Allah above what they describe! Quran (23:91)
He, Whose is the kingdom of the heavens and the earth, and Who did not take to Himself a son, and Who has no associate in the kingdom, and Who created everything, then ordained for it a measure. Quran (25:2)
Jesus died on the cross
And their saying: Surely we have killed the Messiah, Isa [Jesus] son of Marium, the apostle of Allah; and they did not kill him nor did they crucify him, but it appeared to them so (like Isa) and most surely those who differ therein are only in a doubt about it; they have no knowledge respecting it, but only follow a conjecture, and they killed him not for sure Nay! Allah took him up to Himself; and Allah is Mighty, Wise. And there is not one of the followers of the Book but most certainly believes in this before his death, and on the day of resurrection he (Jesus) shall be a witness against them. Quran (4:157)
Saying Jesus is the Son of God means the eternal fire
Certainly they disbelieve who say: Surely Allah, He is the Messiah, son of Marium; and the Messiah said: O Children of Israel! serve Allah, my Lord and your Lord. Surely whoever associates (others) with Allah, then Allah has forbidden to him the garden, and his abode is the fire; and there shall be no helpers for the unjust. Quran (5:72)
For far more erudite and respectful information about this topic I recommend Dr Mark Durie, an Anglican priest from Caulfield Victoria, in a brilliant speech on Youtube: The Abrahamic Fallacy: Why Abraham is not a point of unity for Islam, Judaism, and Christianity.