I don’t have any doubts about the truth of the scripture in the Bible or what it says or who the author truly is.This claim works as long as one believes that the tradition that has been passed down to us is correct. With study of 2nd Temple Judaism though some problems arise. At the time that Jesus lived there were multiple recognized prophesies from the Old Testament regarding the coming Messiah. Several of these, but by no means all, re preserved in the New Testament. But even those preserved in the NT are not consistent with each other, and at least two get amended or ignored by tradition.
Remember, the stated purpose of the gospels, "so that you may believe". Only Luke claims to present the truth, and he was relying on hearsay by his own admission, and the biblical standard for truth tells us that hearsay is not a valid source. It is thus possible that the prophesies that Jesus is recorded as having fulfilled are merely those prophesies that could be justified as having been fulfilled and the others recorded in scripture are clearly not prophesies by human definition. Remember, even Paul admits that he was not the ultimate author of his letters, and many other claimed authors are merely assigned by tradition, so we do not really know who they were or what their connection to God was. We accept much by faith, not fact.
“All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: that the man of God may be perfect, throughly furnished unto all good works.”
2 Timothy 3:16-17 KJV