How Would You Argue That the Unity of the Bible Is Evidence It’s from God?

Questions about how the unity of the Bible can be evidence it’s from God if the books could have been cherry-picked later, whether the fact that some passages in our Bibles aren’t canonical means every part of the Bible can be called into question, and why the Gospels don’t tell who wrote them.   How would you argue that the unity of the Bible is evidence it’s from God? Couldn’t a skeptic object that one could come up with any unified story given enough ancient sources and a good deal of cherry-picking? If certain passages in our Bibles are not true, canonical, or inspired, doesn’t that mean every part of the Bible can be called into question? When I’m asked why the Gospels don’t tell who wrote them, what is the best way to answer?