Much confusion arises from Christian detractors who insists on linking religious beliefs and mass murders of historic proportions. One in particular, suggested by some websites and even argued by a few authors is that Hitler was a Christian (having never renounced his Roman Catholic baptism), maybe even doing "God's work".
Such minority views tend to read into public and some (disputed) private remarks of this butcher without considering the larger context. That larger context was power. Hitler was a determined man with a dream of Aryan dominance over the world and his dominance over the Aryan's themselves.
First of all, the man and his movement were consummate liars. No historian worth his or her salt denies this. Nazis lied publicly in speeches, writing, radio and television, manipulating their leader-starved audiences with what they wanted to hear. They lied privately, manipulating those not within their closest circle of confidants. Political propaganda was brought to an art form in Nazi Germany. Not unlike today, politicians speak the language of the people even while not believing in it.
Secondly, many historians (European and American) acknowledge that Hitler used Christianity to his advantage. He promoted a "Positive Christianity" before the war that cherry-picked various beliefs that would emphasize aggression, activism and strength. The Jewishness of Christ was denied, the sacrificial dimension belittled and the requirement of love redirected toward jingoistic nationalism. He failed to unify the churches with a single lowest-common denominator, nationalistic church.
Thirdly, even if Hitler considered himself a "Christian" at all, it was certainly an unorthodox amalgamation of his own imagination peppered with neo-pagan and higher critical liberal "Christianity" influences (here). It even spawned a German Faith Movement. For Christians serious about their own practice and doctrines, to attack two-thirds of the Bible (the Jewish Old Testament) is to attack Christianity. And to attack the infallibility of the Bible (via higher criticism of the liberals) is to attack Christianity. In Mein Kampf, he wrote,
"with the appearance of Christianity the first spiritual terror entered into the far freer ancient world." (Britannica online)
One may wish to assign Hitler to some form of religion, such as neo-paganism, but orthodox Protestantism is not one of them.
Fourthly, the creation of the Confessing Church which resisted this "positive Christianity" and the politicization of the churches for Nazi ends reinforces the radical differences between Nazi-inspired "Christianity" and the conservative Lutheranism. The Nazi regime itself bullied these churches and the Roman Catholic church with trumped up charges and subtle anti-church propaganda. During the war ministers and priests were cast into concentration camps.
Fifthly, the private inner-circle musing of Hitler, published as "table talk", bespeaks of a man easily throwing around some Christian language while attacking the Christian beliefs and clergy, desiring to suppress organized religion.
Lastly, published de-classified evidence for the Nuremberg trials paints a calculating plan to finish of Christianity after the war (here).
If the ideological and philosophical underpinning of Hitler are taken into consideration, then the opportunistic relationship of Nazism to the churches of Germany makes sense. Dictators cannot change a given society whole-sale in one fell-swoop. Hitler was no exception. His philosophy was influenced by the "God is dead" thinker, Nietzsche (here). In sum, his was a pragmatic will to power philosophy bent on world dominion.
As Hitler's powerful private secretary wrote to the Nazi leaders in 1941:
"All influences that could impair, or even damage, the Fuhrer's and the Party's rule must be eliminated. More and more the Volk [people] must be wrested away from the Churches and their agents, the pastors." (Library of Congress WWII Companion, p.903)