When addressing the then disciples and future Apostles Jesus said this and I believe it menat something: Joh 15:15 Henceforth I call you not servants; for the servant knoweth not what his lord doeth: but I have called you friends; for all things that I have heard of my Father I have made known unto you. Joh 15:16 Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you.
I believe when they cannonized the Bible all of the questions of authenticity and what not were taken into account. Luke did a pretty good job. He actually got 2 books voted in.
And I think he was a Gentile.
I think it is because they must have found something in those other seven books that they could not verify. All of the books that were allowed in the cannon were verifiable and true.
Those other 7 books may have some very good information in them but there was something there that was unverifiable. Whether Luke was a prophet or not has no bearing if his writings were inspired. If we were to question this then why don't we question the whole Bible. The book of Matthew was written around 60 A.D. How do we know what Matthew wrote about Jesus is actually true. It was written about 30 years after Jesus' death. Try to remember accurately something that happened in your life 30 years ago.