D is the designation for the Deuteronomic source, a layer of the Pentateuch in the Documentary Hypothesis. The D source is largely restricted to the book of Deuteronomy and is generally dated to the 7th century. The D source is also generally associated with the “book of the law” that was “discovered” in the temple during Josiah’s reforms. Although an edition of the book is associated with Josiah’s reforms, it also considered to have earlier antecedents with some association with the northern kingdom. D has similarities to E, both sharing Horeb, and D shows an intentional and explicit reworking of the laws found in the Covenant Code, which is mostly from the E source (though the existence of an independent E source has been questioned). D is also reflective of Josianic reforms by its centralization of worship, not naming the site, presumably because it is set during Moses era. The rejection of sacrifice outside of Jerusalem is an important for ordering Pentateuchal layers, since it is often argued that JE know no centralization, D argues for it, and P presumes it. D’s theology of centralization, its theology of retribution become important to the Deuteronomistic school, which is thought to be responsible for works like the DH and Jeremiah.
Coogan, The Old Testament