1) the Quran (2:29) says that the Heavens are seven in number, while "Barnabas" gives the number as nine (178).
2) according to "Barnabas", man is endowed with a free will. (164). On the contrary, man only does what Allah wills him to do (Quran - 76:30, 37:96, 17:13, 10:99-100).
3) Adam was not the first man circumcised (23). Abraham was.
4) according to "Barnabas" (3), Mary brought forth her son without pain. This is contradicted by the Quran (19:23).
5) the Quran follows the Mosaic law of "an eye for an eye, and a tooth for a tooth", whereas "Barnabas" says "... ye shall not overcome evil with evil, but rather with good" (81). "Woe unto them that call for vengeance ..." (63). "... kiss the hand of those who revile thee, and present gifts to those who persecute thee and strike thee much" (64).
6) the Quran approves of poligamy. "Barnabas" does not tolerate it (115).
7) the Quran approves of the teaching of abrogation. "Barnabas" condemns it (38).
8) the Quran condemns eating pork but "Barnabas" says "that which entereth into the man defileth not the man, but that which cometh out of the man defileth the man" (32).
9) "Barnabas" totally ignores the existence of the prophet John the Baptist (Yahya ibn Zakariyya).
10) according to "Barnabas", Jesus expressly denies that he is the Messiah. In the Quran, the only Messiah is Jesus.
Still, "Barnabas" further compounds his confusion. For while he has Jesus denying that He is the Messiah, yet, amazingly, the first words of "Barnabas" following his introductory title, read:
Barnabas, apostle of Jesus the Nazarene, called Christ ...
According to "Barnabas", then, Jesus is called Christ, but he is not called Messiah. Despite his obvious familiarity with the Bible, "Barnabas" does not know that Messiah (Hebrew) and Christ (Greek) are identical in meaning.
Internal evidence shows that "Barnabas" was not a contempory of Jesus:
a) In chapter 82, "Barnabas" makes the jubilee a centenary event. The Jewish jubilee, it will be remembered, was celebrated every 50 years.
b) Quotations from Dante are another evidence proving a late authorship of this "gospel". They cannot be accidental coincidences, since they are of great number. Of these I can mention a verse which is clearly a quotation of Dante: "they go and serve false and lying gods", which has been quoted by "Barnabas" in two places (78, 217). The expression, "raging hunger" (60) is probably another specimen of such a direct quote.
The description of the joys of paradise and the horrors of hell, and the pains which the unbelievers suffer in the latter, recall us to Dante's descriptions of the same. (Compare "Barnabas" 59 and 60 with lines 22 and 103, Canto III of Dante's Inferno).
Stranger still is the coincidence between Dante's 'circles' of hell and those of "Barnabas". "Barnabas" has Jesus saying to Peter:
Know ye therefore, that hell is one, yet hath seven centres one below another. Hence, even as sin is of seven kinds, for as seven gates of hell hath satan generated it; so are there seven punishments therein. (135)
This is exactly what Dante says in Canto V, VI, etc. of his Inferno.
Again, "Barnabas" says that God, having created the human senses, condemned them "to hell and to intolerable snow and ice" (106). See Dante's Inferno, Canto XXVIII and III, line 22.
But still stronger evidence that "Barnabas" quotes directly or indirectly from Dante is his description of the "geography of Heaven". Here "Barnabas" agrees with Dante and contradicts the Quran.
c) Traces of Medieval Society
Among the clearest of all these traces are those of the system of feudalism, which was in full vogue in medieval times. According to this system land was divided among the different feudal lords, who in turn subdivided their property into minor divisions and rented them to vassals who owed them a perpetual allegiance, above all, in times of war. The writer of the "Gospel of Barnabas" represents to us Mary, Martha, and Lazarus as feudal lords, in whose hands was the proprietorship of whole villages (194).
This is a further description of the vassal who owes to his liege or padrone a portion of his crop (122). This is quite in accordance with the laws of feudalism.
The reference to wine-casks is more suggestive of Italy than of Oriental lands (152).
Another trace is that referring to medieval court procedure where the arrested prisoner is questioned by a magistrate, while a notary jots down memoranda of the evidence (121).
The reference to the duel between two rival lovers reminds one of the age of chivalry (99). It will be remembered that chivalry was a creation of medieval society and played its role for a considerable period.
d) Barnabas' ignorance of Palestinian geography and history
"Barnabas" imagines Nazareth, and most probably Jerusalem also, to be on a sea or lake. "Jesus went to the Sea of Galilee, and having embarked on a ship sailed to his city of Nazareth" (20).
"Having arrived at the city of Nazareth the seamen spread through all the city all that Jesus had wrought" (20). Here it is clearly meant that immediately on touching land (Nazareth), the seamen landed and spread their news in that (seaport) town!
"Barnabas" then says: "Jesus went up to Capernaum" (from Nazareth) (21). Of course, it is just the reverse. He would have landed at Capernaum, gone up to Nazareth, and then gone down to Capernaum.
We are told that one Sabbath morning Jesus came to Nazareth (143). After several chapters giving his conversation there (144-151), we read: "Jesus embarked on a ship ... (151). This is further evidence for Barnabas' wrong notion that Nazareth was on the lake.
There is still more. The ship leaves the port of Nazareth and sails away. Where do we find Jesus next? At Jerusalem. In the very next section we read: "Jesus having come to Jerusalem ..." (152). There can be little doubt that as the ship weighed anchor at Nazareth, so it cast the same at Jerusalem.
Next we come to some incidents recorded by "Barnabas" which are historically untenable. There is the story of Daniel, who, according to "Barnabas" (80), was taken captive by Nebuchadnezer while he was yet 2 years old. Now if we suppose that Nebuchadnezer captured Daniel in the first year of his reign, it would follow that in the second year of his reign, Daniel was three years old. In this very year, it will be remembered, he was promoted by Nebuchadnezer to the rank of a ruler "over the whole province of Babylon". According to "Barnabas" therefore, his age would be three, at most four years!
"Barnabas" tells us that a great sedition broke out in all Judea on account of Jesus (91). It is unnecessary to remark that this incident finds no place in the pages of any historian, whether Josephus, or any ancient or modern historian. Besides, it is absurd to believe that 3 armies, numbering 600,000 soldiers, could gather in the twinkle of an eye and disperse as quickly. And how can we believe that Herod, an enemy of Christ, would attempt to quiet a riot which arose on account of Christ?
Stranger is the statement of "Barnabas" that the high priest wished "to bow himself down and worship Jesus ..." (93). The high priest, it will be remembered, was the chief enemy of Jesus and one of his accusers who condemned Jesus because Jesus used to convict the high priests of hypocrisy.
He who is aware of its contents, yet continues to maintain its integrity and to utilize it as a genuine gospel account of Jesus at the expense of the Bible, must share in the guilt of the author.
To my mind, looking at the evidence (only a fraction here), It is as George Sale put it a "bare-faced forgery".
Muslims only undermine their credibility when trying to bolster their cause using it.