Dear Michaela,
This could be the original reason as to why Pehar/Nechung, of all deities, was chosen by the 5th Dalai Lama to be the "official state oracle".
"The question soon arises as to why of all gods Pehar, the former ferocious and cruel opponent of the Land of Snows, was given the delicate office of being a supernatural governmental advisor to the Tibetan “god-king”. Surely this would have sooner been the entitlement of a Bodhisattva like Avalokiteshvara or a national hero like Gesar of Ling.
With this question too, the key is to be sought in the “political theology” of the “Great Fifth”.
We may recall that both the conferring of the title of Dalai Lama and the establishment of the hierarch’s secular power were the actions of the Mongolians and not of the Tibetan people. In contrast, as we have reported, in the 17th century the national forces of the country were actually gathered under the kings of Tsang and around the throne of the Karmapa (the leader of the “red” Kagyupa sect).
Thus, it does not take much fantasy to be able to sketch out why Pehar was chosen as the advisor of the “yellow” Buddhist state (then represented by the Fifth Dalai Lama). It was expected of the former Mongolian god and opponent of Tibet that he tame the recalcitrant Tibetans (who supported the Karmapa). In this his interests were in complete accord with those of the “god-king”.
Additionally, the “Great Fifth” himself was a descendant of an aristocratic family which traced its lineage back to the Hor Mongols.
Pehar, the later state oracle, is thus a foreign deity imposed upon the Tibetan people."
Source:
http://www.bibliotecapleyades.net/sociopolitica/dalai_lama/Part-2-07.htm