I think it is pretty obvious why some claim the 10 virgin parable does not refer to Christians. It is the same old struggle that even Martin Luther had. At some point the their theory breaks down. For Luther it was the book of James and the scripture faith without works is dead. He wanted to exclude this book. The book of James is a great warning to those would be hypocritical christians who think nothing of them is required. In a similar way the pharesees thought they had it made because they performed on the surface, but God wants the heart. That is why there are 5 foolish ones who did not realy give Jesus their heart. It was a shallow profession that denied any personal commitment or relationship. That is why he says depart from me I never knew you.