(Aside before I begin: please assume that all claims about identity, superiority, etc. are put in heavy quotes here. Also, I'm coming at this from my study of 19th/20th century spiritual movements and art, so of course other approaches are very valued!)

What an interesting question! Let me start by saying it is very unlikely that Ehrler had a literal belief in Valhalla, but the use of pagan/Teutonic motifs was very common in Germany as originating in the völkisch movement. In short, the popularization of Germanic/Teutonic/Norse symbolism and identity was seen as a way to unify Germanic identity, retain German pride (especially after the tremendous national trauma of 1918), and glorify Germans over their neighbors--especially those who had beaten them in the First World War. As an example, Richard Wagner was very popular in Germany at this time; his Der Ring des Nibelungen (The Ring of the Nibelungs) is set in Norse sagas. We'll come back to Wagner in a minute.

The völkisch (roughly, ethno-national) movement can trace its rise back to the early 19th century. As other Nationalist Romantic movements, it emphasized ethnic unity and the "pure" identity of those who belonged to that "blood." As such, it played a large role in the cultural unification of Germany. It claimed to support a nobler, more ideal way of life that returned to the better culture of the past: it was anti-urban and anti-intellectual (both of which were identified with Jewishness). As has been thoroughly remarked upon, there was a distinction made between Kultur and Zivilisation, with Germans embracing the former. Kultur was strong, proud, simple, and clean, embracing emotion and honesty. Zivilisation, represented as more French and Anglo-Saxon, was too interested in intellectualism and properness. Martin Ignatius Gaughan writes about that in 1910, Prussia proposed designating "Kulturträger," bearers of culture, to have special privileges, having "completed a minimum of three years of study at a university, had passed the state examinations in his field, or one who had served the sstate as an official or as an army officer." To quote Gaughan, "The Kulturträger would be the bearer of Kultur, of those profound cultural values specific to the German tradition, in contrast to those shallow values of Zivilisation, the products of the modernising process as it developed in Western Europe, that is, in Britain and France (and the United States)" (15). In 1939, Norbert Elias published Sociogenesis of the Antithesis Between Kultur and Zivilisation in German Usage. Again, quoting Gaughan, in Elias "The concept 'Zivilisation' can encompass values that are political, economic, religious, or technical, related to moral or social issues, but 'Kultur' essentially concerns itself with spiritual, artistic, religious issues, and tends to draw a sharp distinction between these and the political, economic, and social" (16). It was proposed that Germany's late unification demonstrated that the Germanic people had traveled a different path (Sonderweg) to modernization. The Germans were, this argued, essentially different from their neighbors to the West.

Why was this so important? This cultural movement had a tremendous influence on German national identity and was widely used in progaganda to both demonstrate the superiority of the German people and to motivate Germans to fight against the so-called inferior races. I would point to two major events: the unification of Germany in the 19th century and the disastrous events of the First World War. The unification, as I have mentioned, brought with it a new emphasis on German identity, forged explicitly in contrast with those of other countries. There was a renewed interest in Germanic paganism, in returning to nature, in sports and physical exercise, and in the history and archaeology of the Germanic peoples. All of this became infused with the spiritualist Theosophical movement, creating the branch of Ariosophy in the late 19th/early 20th century, which combined the ideas of a mystical origin of the human species which progressed from early to later "root races" with ethnic identity: the Aryan race was, they declared, the most advanced of the races, and from them would emerge an even higher, better race. According to this theory, the Norse and Germanic people were the same race, and they shared a common culture and future. These ideas spread throughout Germany and were widely used in Nazi symbolism. The Ahnenerbe was created in 1935, an archaeological project that aimed partially to research the history of the "Nordic" race. (Here I should stress that these pagan ideas were used as symbols, NOT taught as a religion: I could go into the claims about Nazi occultism, but suffice it to say these are mostly postwar fictions.) This cultural movement brought with it the celebration of traditional holidays such as the solstice, a revival of folk dress and folk dance, and a renewed interest in old sagas. In an example with interesting connections to your question, in the German propaganda film Stuka, a pilot experiencing shell shock after his traumatic experiences in the war watches the final cycle of Wagner's Der Ring des Nibelungen and is reinvigorated with love for his country so he overcomes his shellshock (!!) and goes off to happily bomb England.

This, perhaps, has been a bit of a long way around, but I hope I have been able to show why Norse pagan symbolism was so prevalent in Germany in this era.

Cited: Martin Ignatius Gaughan, German Art 1907-1937: Modernism and Modernisation Oxford: Peter Lang, 2007.

Futher reading: Joseph Bendersky, A Concise History of Nazi Germany, 2014 (4th ed.) E Kurlander, "Hitler's Monsters: The Occult Roots of Nazism and the Emergence of the Nazi 'Supernatural Imaginary'", German History Dec. 2012.

And I'd be curious as to the opinion of others on Nicholas Goodrick-Clarke's The Occult Roots of Nazism, which I've seen varying opinions of.