Was Adolf Hitler a Christian? Was he, as others charge, an atheist? 
These questions are poorly formed. A more apt question would be, ‘What did he ‘believe’ beyond his own destiny, if anything?’
A preliminary point that needs to be made concerns the touchy question about which scholars one trusts and which one does not; but I don’t really want to raise that issue. Nonetheless, a rule of thumb is, if the same historical trend has been noted independently by different scholars giving careful interpretation of the source materials, then likely their remarks can be trusted, and any disagreements resolved through consideration of their differing perspectives. The majority of scholars I’m familiar with agree that Nazi Germany, and the Nazis themselves, were not as religiously homogenous. Hitler’s own beliefs depend on a careful study of Mein Kampf – selected passages will mean nothing taken out of context.
Such a move leaves one utterly unable to account for the complexities of Hitler’s psychology; unable to account for his biography, what led him to the juncture that Mein Kampf marks as the arrival of the historical Hitler; unable to account for the complex relationship Hitler had with the German right and the German people as a whole. It will certainly not adequately account for the anti-Semitism; or for the obvious tensions between Hitler’s own cosmogony and that of Christianity, which are not identical and in many respects antagonistic.
Quite a number of scholars believe that the evidence strongly suggests that the Nazis not only intended to re-interpret Christianity, but do away with it entirely. (The ‘bible’ they placed on the alter of the one church they established themselves, in Berlin, was of course – Mein Kampf.) That doesn’t make them atheists, but I never said it did. The matter needs greater study, more complex and nuanced argument, greater accounting of the historical context. The problem at the time was not simply Nazism, nor religion, but the history of Germany to that date, and the malaise the Germans found themselves in during the 1920s. The issue simply cannot be reduced to a question of whether they had a religion or not. They had Hitler.
What Hitler himself seems to have believed about himself and his place in the world, is that Fate – some cosmic force, which he sometimes equates with ‘the Almighty,’ but also simply refers to as a less personalized ‘Fate’ or ‘Destiny’ – had placed him at the epicenter of an age old racially determined struggle between the Aryan and the Jew. ‘Good’ (Aryan) and ‘evil’ (Jew) are entirely defined by this struggle, there is no morality otherwise.  His dedication to this struggle effectively became his religion.
Thus, Hitler’s own profound sense of personal destiny and his rage against the Jews led to his religion – not the other way around.
Mein Kampf is an act of self-creation. It’s a passion, a narrative of apotheosis of a self-identified savant and savior.
After the disappointment of the Beer Hall Putsch, Hitler wanted to trash the established right-wing, with its old militarism, and re-define Nazism as a holistic anti-Semitic revolution, and at the same time culminate the reconstruction of his personality that had been on-going after his nervous collapse at (and as response to) the end of WWI. This meant providing an entire cosmogony that could synthesize with both traditional beliefs and prejudices as well as then-contemporary popular understandings of scientific knowledge. It also meant providing a mythic figure that could function as both prophet and savior – Hitler himself, of course.
It is not at all clear what Hitler really thought about the trends of belief that came before him, whether that which could be found in traditional churches, or the developments of science. Paganism, eugenics, Weimar hedonism, evangelical tent-revivals, blind faith in technological innovation, paranoid denial of then current physics – all were simply melted into the alloy forged in the furnace of Hitler’s rage against the world (where he had only felt belonging as a soldier during during the First World War [3}). (A close reading of Mein Kampf reveals that he actually held Germans in contempt almost as much as Jews – “Are these still human beings, worthy of being part of a great nation?” he allows himself to wonder in evident disgust, concerning the German construction workers with whom he worked before the war. ) Hitler’s racism was conditioned by Social Darwinism as well as by ‘special creation’ theories, since both were prevalent in that day; but originated in his personal disgust with the human, and his experience of the world as little more than a battleground in a war of all against all.
Claiming to know “what Hitler believed” is simply facile, without struggling to grasp who this cypher was  or why his speeches resonated so well with the Germans of his day. It is also a misconception of modern revolutions to try to define their attempts to supplant previous religious beliefs with their preferred ideology, as reducible to the imperatives of their ideology. It is in the nature of modern revolution itself to supplant and dissolve traditional religion. This is as true of ISIS as it was true of the French Revolution’s “Church of Reason.” And it was certainly true of Hitler’s self-created messianism. Of course Hitler would find it useful to claim the authority of “the All-Mighty” for his project. But beyond some profound sense of personal destiny, it is wholly unclear that Hitler believed there was anything ‘out there’ but chaos and never-ending conflict. Although Hitler courted the Wagner family to lay claim on Nietzsche, in fact the only philosopher he read was Schopenhauer (although he inverted Schopenhauer’s understanding of Will as what needed to be constrained, choosing instead to unleash it).
So what did Hitler believe? I have tried to suggest here that, while the question is most certainly interesting, answers to it cannot be reduced to ‘ready-mades’ to fit our own ideological preferences. He was a product of history – but that history was not simple, not linear, and not uni-vocal. Like most of history, it was – and remains – a morass of conflicting urges and social pressures against the individual’s will to achieve some importance – some sense of ‘being there.’
That’s the problem – the will to become a self in opposition to all other selves.
Any ideology promising that will only bring about heart-break.
 Really, the dangling of the ‘Hitler-monster’ in the theist/ atheist god debate has got to stop. It does no justice to the victims of Nazism, and distorts the history rather than clarifying it. ‘Well, they started it!’ each side claims – I don’t care. It’s got to stop. It is poorly informed, a-historical, and contributes to the general stock of discursive muddle that plagues the public mind, especially on the internet. Those who think they really have a case to make, should engage in the research necessary to make that case, and not mine for quotes. As raw source, Hitler can be made to say practically anything. Anyway, the whole “believers in X do nasty things, therefore X is wrong,” is a bad argument. Every ideology contains imperatives that can be used to justify even heinous acts. The real lesson of Hitler here is that, if one wants to perform those acts, one will find the justification for it – or make it up.
[2} See: Lucy S. Dawidowicz, The war against the Jews, 1933-1945. Weidenfeld And Nicolson (1975).
 See: Kenneth Burke, “The Rhetoric of Hitler’s Battle” in The Philosophy of Literary Form: Studies in Symbolic Action. Vintage. pp. 191-220. Reprinted Berkeley, California: University of California Press(1974).
 Adolf Hitler, Mein Kampf. Translated and edited by Alvin Johnson et.al., Reynal & Hitchcock (1941); page 54.
 See: Joachim C Fest, Hitler. Translated by Richard and Clara Winston, Harcourt (1973).