Dead Sea Scrolls: a people still producing scripture-like texts
Qumran copied Moses and the prophets and also wrote pesharim, the Temple Scroll, Hodayot, and 1 Enoch. They did not act like a community whose God had finished speaking when Malachi died.
The closed Protestant canon is a decision of later churches, not a verse in the Bible. Deuteronomy 4:2 and Revelation 22:18–19 each protect the book in which they appear. If Deuteronomy closed the canon, we would have no Isaiah, no Gospels, and no Paul. The Restoration simply refuses to do to the New Testament what no one should have done to Deuteronomy.

