Why did Adolf Hitler hate Jews?
Unfortunately the correct answer to this requires several paragraphs, so bear with me:
In the 19th cent., industry developed rapidly with overwhelming force in the developed Western countries, especially England and the US. Germany was a bit late to join the crowd, not starting its industrialization until the latter half of the century but by the end of the century it too was almost on par with its English cousins. However, one prominent (or, soon-to-be-prominent) nation was not invited to the party: Russia. Russia did not begin industrialization until the 20th century and consequently was at a significant disadvantage which is manifested by its lack of capturing any colonies. Another factor working to its detriment was that it was culturally a more backward country. It only established nationhood in the late middle ages and so it did not have the same cultural, artistic, legal and religious experience as its western neighbors.
This dichotomy between the "east" (Russia) and the "west" (France, England, Germany, US, etc...) wasn't very evident at first but when Bismarck's moderate policies were thrown out the window in favor of assertion of German nationalism, things escalated precipitously into world war I pretty fast. World war I was fought primarily between the Germans and the Russians; in other words, between the west and the east.
Why was Germany so irate at Russia?
The Russians, as discussed earlier, did not have strong industry established. Consequently, Communism was much more appealing to them as a nation than it was to Germans as a nation. Furthermore, in order to fully reap the benefits of communism the weak Russian state had to convince other states to join the fray and establish an international society of workers where no nationality would be recognized. Such a system definitely would benefit the have-not Russians by diverting the benefits of capital in the west to the "soviet workers" in the east. Thus it is clear that the Russians would ethnically come out ahead if Europe was just one big communist state whereas Germany would come out ahead by resisting the transfer of its capitalist wealth to the workers in the east. This is essentially the underpinning of world war I.
In theory, the West should have sided with Germany in this "Great War" (as it was called back then). Indeed, some Americans and English did favor Germany at first or remained neutral. It is the French who got us involved in favor of the Russian side because the French felt very threatened by the expansionist and aggressive tendencies of the newly unified German state. Also, the french were Catholics and so bore some strong resentment against the protestant Germans and vice versa. Somehow, even though the French and English had been fighting non-stop for the past 300 years they decided to put their differences aside here and the French convinced the English that the Germans were a threat to the established political and economic institutions of Europe. (After all, France and England are kind of like sisters ever since the Norman invasion compared to their "cousin" Germany whose culture branched off much earlier and had no direct interaction with Franco-English society after the Norman invasion.) The Germans probably screwed up themselves as well by antagonizing the Americans through sinking their merchant vessels on high seas. This prompted the Americans to side with their English sisters, even though, that meant they were supporting Russia against the "West" (=Germany).
The Germans lost the war, not because its western allies liked Russia any more than Germany but because it momentarily feared German aggression more than Russian communism. Hitler was born into a low-level Austrian (=Prussian) family. He wasn't really "German" and did not belong to the landed aristocracy or to the indsutrialist-capitalist class; his personal education was also a big mess. He became a rebel in High school deciding to be a "hipster artist" (in modern parlance) as opposed to completing a normal education and pursuing a traditional semi-skilled career (such as a customs official -- which is what his father did and what he wanted his son to do). Lack of education lead him to combine two very strange and opposing interests into one. On the one hand he championed worker's solidarity and sought to bolster their interests (which seems to go along well with the Russian trend of global communism) but on the other hand he insisted on "nationalism". He only wanted "Aryans" to participate in this worker's society. In due time the emphasis on workers was minimized and that on the "nation" was maximized. In effect, this poor, uneducated German found himself fighting the cause of Germany's aristocratic nationality in the face of the soviet "poor man's" global society. How bizarre! There's no question that had he been more educated he would never have embraced such a stance.
In order to promote German nationality in face of the communist dogma of globalism, he had to define the term. Instead of defining himself with positives, he --like other ignorant bigots have done throughout history-- defined himself with negatives: what the Germans were not. The Germans are obviously Not Slavs; but who are the Slavs? The Slavs in post WWI Europe were the one people who completely disregarded religion. The Slavs were the ones who did not distinguish between Jew and christian since in their view both religions were crap: just capitalist propaganda. The Russian society was the one in which Jews gained prominent political as well as socio-economic positions as opposed to German society where Jews never had attained political prominence even after the enlightenment. "Okay", Hitler said, "So, to be opposed to the Slavs one had to be opposed to the Jews". There were no Slavs interwoven within German society but the Jews were well connected, especially economically and professionally. Hitler insisted that he "clean home" first. He viewed the Jews as the traitors who "sold out the Germans" by agreeing to most humiliating peace terms in the treaty of Versailles (which settled WWI) even though, Hitler believed, Germany was perfectly capable of continuing and winning the war. He referred to them as the November Criminals (after the month in which the treaty was signed).
Were the Jews really responsible for the humiliating terms of the Treaty of Versailles?
In the true sense of the word, of course not! But is there some connection between Germany's defeat in WWI and Jewish triumph? Yes!! Remember that the Jews NEVER had any landed property through the Middle ages. This pretty much ensured their status as "paupers" to which the church had deliberately relegated them. Naturally, then, the Jews as an ethnic group stood to gain tremendously from communism. Indeed, the German communist party at the time consisted entirely of Jews. The only reason this explanation is somewhat puzzling is the fact that Hitler himself hailed from the low class and if he had to excel using a traditional path, he would have never made it given his lack of established money, political connections and noble origin. Thus, theoretically speaking he actually should have had more in common with the Jews than with the typical empowered German. But, like I said: he did not properly comprehend the dynamics at play in the Prussian-German state, which lead him to staunchly identify with "national" interests against "class" interests.