The first mention in historical writings of the 'gospel of Barnabas' was in the 17th Century.  Most scholars agree that it was written in the 14th or 15th Century, well over a 1000 years after Jesus (or Barnabas) existed!  In short, it is of little value as a historical account, and of no value if you want to discover the truth about Jesus Christ.

The four gospels of Matthew, Mark, Luke and John on the other hand, are written very close to the lifetime of Jesus, entirely reliable, and contain all the truth that we need concerning Jesus' birth, life, death, resurrection and ascension; and the reasons why we should put our faith in Jesus.