As has been said one of the first things to point out would be that the Bible is a collection of books with many different authors, since many people do not realise this.

I would try to explain how the Bible came to be commonly accepted (more or less) in the form that it is today, and obviously Judaism will be just as important as Christianity in that respect. Go into how the unification of Israel/Judah led to the old scrolls being rediscovered, then how they were compiled in captivity in Babylon etc.The Bible is about 80% Old Testament after all, getting across that perspective is pretty important since a lot of people don't appreciate that.

And of course for the New Testament you would go into Athanasius etc.

I would also try to explain to the audience how the Old and New Testaments relate to each other. Most importantly would be the idea for Christians that the Old Testament is generally understood in light of the New Testament. As opposed to being made obsolete or being outright contradictory (in their perspective).