Moses says in Deuteronomy 4[:2], “You shall not add anything to the word which I speak to you, nor take anything from it.”
Now some will say that Moses here speaks only of his own word, for many books of the prophets as well as the entire New Testament have been added beyhond the books of Moses. I reply: Nevertheless nothing new has been added, for the same thing that is found in the books of Moses is found also in the others. These other books, while using different words and narratives, do nothing more than illustrate how the word of Moses has been kept or not kept. Throughout them all there is one and the same teaching and thought. And here we can challenge them to show us one word in all the books outside those of Moses tha
t is not already found in the books of Moses. For this much is beyond question, that all the Scriptures point to Christ alone. Indeed in John 5[:46] Christ says, “Moses wrote of me.” Therefore everything in the other books is already in the books of Moses, as in a basic source.
Luther, Martin Luther’s Works 35, American Edition 132