There are many theories regarding Hitler's hatred of the Jewish people. One of these reasons is mere jealously. The Jewish people were not hit hard during the Great Depression and Germany was hit the hardest. Hitler also blamed Germany's defeat in WWI on the Jewish people. Also, some blamed the Jewish for the "Treaty of Versailles" which was very damaging to the Germans.
The idea of the Aryan German race was also to blame for Hitler's hatred of Jewish people because they were not part of the ideal white race that Hitler envisioned.
In addition, Hitler supposedly had a bad experience as child with Jewish people and this is when the hatred was seeded.
These are just a few of the theories why Hitler hated Jewish people so much. There are many many more.