Anyone trying to establish a new religion will need to discredit or explain away prevailing belief systems. Muhammed, the founder of Islam, lived at a time when the old Arabic religions had fallen into disrepute. Christianity was making many converts among the Arabs. So when Muhammed proclaimed himself a prophet and invented a new religion for his people, he designed with built-in defenses against Christianity and Judaism, his chief competitors. The Quran makes many statements about Jesus which contradict the New Testament. Muhammed seized upon Jewish arguments against Christianity, chiefly the idea that Jesus was misunderstood and never claimed to be the Messiah or the Son of God.
The Barnabas gospel was discovered in the early 18th century by a Prussian courtier named J.F. Cramer. It exists in a number of manuscript versions, none older than the late 16th century. There is a Spanish version with a "find story" stating that a monk by the name Fra Marino found it in the library of Pope Sixtus V while the Pope was taking a nap. The monk read it and promptly converted to Islam; this story is not very believable and has a curious parallel in the Barnabas gospel itself, where Nikodemus is said to have found the original Book of Moses in the high priest's house while the priest took a nap.
The Barnabas gospels' outline of Jesus' life resembles the canonic gospels, but everything has been altered to conform with what the Quran says about Jesus. One could say that this is a "gospel for Moslems". When it was first printed in an English translation in 1907, it aroused great interest in the islamic world and an Arabic version was published in 1908. Since then there have been numerous Arabic editions. Literary historians and Bible scholars agree that this pseudo-gospel was written sometime in the later Middle Ages by a former Christian -- probably Italian -- who had converted to Islam. It has not received much attention in the Western hemisphere, but caters to Moslem wishful thinking and is taken seriously in the lands of Islam.