But if we wanted to try to step out of this postmodern mindset and see something more timeless, what would we see the Bible claiming for itself (i.e., what is its "self-witness")? John Frame, a good and dependable teacher, says,
"...the Bible... is first and foremost...a book about God, about Christ, about the salvation of man from sin. But that message of salvation includes a message about the Bible. For this salvation requires verbal revelation. In saving man, God speaks to him..." (http://www.frame-poythress.org/scripture-speaks-for-itself/).
I recommend that article as a very good explanation of what's at stake in understanding the role of Scripture.