Was this "discovery" a pious fraud?
As long ago as 1805, WML De Wette suggested that Deuteronomy was far from being an old relic of Moses lost for a long time and then found by Hilkiah. Rather, said De Wette, Deuteronomy was composed not long before it was “found” in the Temple, and this “finding” was a charade. Perhaps Hilkiah wrote it himself, either alone or in conjunction with Josiah to provide a pretext for the reforms that followed. It has also been suggested that to legitimise these measures, the scribe of what we now have as the Covenant Edition even retrospectively invented the notion of a previous covenant concluded in the land of Moab when Israel was about to enter the Promised Land (Deut 28:69) to serve as a historical precedent for Josiah’s covenant with the people.
Josiah’s reform’s main objective was to centralise the Yahweh cult in the temple at Jerusalem on the basis that just as Yahweh is one, so his Temple must be one, and Israel may worship Him only at the one site: Jerusalem. But close inspection of the text reveals that it was written after the event and that the scribe was reflecting on it after the event. The Covenant Edition contains a theological reflection on the reform and a resume of a variety of laws, some of which are only remotely related to the centralised nature of the reform itself, such as the rules on clean and unclean animals, which are then re-considered in the light of the reform: Deut 12:1 – 16:17.
According to Van der Toorn, the scribe behind the Covenant Edition was most probably a legal scholar and theologian rather than a politician or pamphleteer. Cloaked with the authority of Moses, the lawgiver of old, he reinterpreted, adapted, and rewrote the legal traditions he was familiar with. On another level, Hilkiah's written scroll served as the catalyst for Josiah’s religious reforms and thus endowed the realm of writing religious texts with a new social perspective. It signified that writing had broken free of state control and was now in the social domain of the priests and temple that could use the written text as a tool for religious reform[1].
[1] Freeman, op cit.