Satanus, Judaism, which is not based in the Old Testament but the Talmud and the Kabbalah, is very different from Christianity. Judaism is monistic while Christianity is dualistic. There is no harmony between the Old Testament and the Talmud. Judaism was created in reaction to Christianity. That's why Judaism has been a revolutionary force in the world for more than 2,000 years.
An example of Judaism's monism is in the Kabbalah, which views good and evil as coming from the same source, being equal and necessary for the elevation of man to divinity (the source of the chosen race complex for both Judaism and Nazism). The obvious result of this belief is that engaging in evil is not considered "bad" but necessary. The ends justifies the means.
Christianity, on the other hand, sees good and evil as deriving from different sources, or more specifically, evil derives from the lack of God, and God is totally sovereign. The Old Testament is also, of course, dualistic. In Christianity, God has no part in evil and, instead, distances Himself from it. For to partake in evil would compromise His very being, His nature.