Question:

What about the Gospel of Barnabus? Who write it? For what? Was Barnabus is
apostle or not?

Answer:

My answer will depend on whether you mean the Epistle of Barnabas or the
Gospel of Barnabas. Of the two, the more well known is the Epistle
(letter) of Barnabas.

The question of whether Barnabas was an apostle is an interesting one. He
was not one of the original twelve. Nor was he appointed as an apostle in
the usual sense of an original witness to Jesus at a later time (as was
Matthias in Acts chapter one). Nevertheless, he is labeled as an apostle
in many early church writings. The New Testament implies that even in the
times of Paul, men beyond the twelve were widely named apostles by the
church. The word apostle means, literally, messenger. Some have claimed
that Barnabas was one of the commissioned 72 that Jesus sent out. There
is no direct evidence for this. So, whether or not Barnabas was an apostle
depends on your definition. By the traditional, biblical definition (Acts
1:21-22), he was not an apostle.

Let me first answer assuming you mean the Epistle. The answer is that we
do not know who wrote the Epistle of Barnabas. It was almost certainly
not written by the famous Barnabas, friend and traveling campanion of
Paul, although some have defended his authorship of the letter. The date
of writing is not known, but it almost certainly was written before AD 132
(because it appears to predate the Bar Kochba rebellion in Jerusalem), and
quite likely as early as AD 100. It was included in an appendix to the
Codex Sinaiticus, a manuscript of about AD 350, showing that this letter
was held in very high regard. The letter was written to oppose Jewish
thinking and reliance on the Old Covenant law for salvation. This book
shows that Jesus Christ is foreshadowed and prefigured throughout the Old
Testament. It is intended to show the glory of the New Covenant and its
replacement of the first covenant of Moses. I would invite you to read
this letter. Just find it in Google! I find it to be a good letter, with
excellent insight into Old Testament prefigures, even if it is almost
certainly pseudepinomous (in other words, is not written by the person
after whom it is named).

About the Gospel of Barnabus, this letter is of much later date and is of
little if any value for a Christian to study, except as a curiosity to
understand the thinking of certain groups hundreds of years after Christ.
Scholars attribute this book to an Italian who became a Muslim. It
reinterprets the gospel message in a way which is in concordance with
Islamic teaching, which clearly makes it a much later composition.

John Oakes, PhD