It is very important to understand the difference between the Jewish understanding of Satan and the Christian understanding of Satan. First of all, in doing a quick search of the Hebrew and Christian bibles, we find a remarkable difference. In the Jewish bible (Tanakh), we find three separate references to Satan (the book of Job is considered one reference because it is one continuous story). However, in the New Testament, a book 1/3 the size of the Hebrew bible, we find 35 references to Satan. If we add the word devil to the search, we get an additional 32 references in the New Testament. In total, a search using different euphemisms for Satan leaves us with well over a hundred references. So, the first thing we need to understand is that in Judaism, HaSatan is not a main focus of our relationship with HaShem (G-d). Whereas, Christianity almost seems preoccupied with him.
This applies only to passages referring to Satan as a proper name the angelic being. The word Satan is actually used many times in the Tanakh, and it means an adversary, obstacle or stumbling block.
Besides the shear pre-occupation with Satan, we find another very major, fundamental difference between the Jewish understanding of Satan and the Christian understanding of him.
In Christianity, Satan is an enemy of G-d, an opposing force, and something very bad. In Christianity, Satan has a level of power that is considered almost equal to that of G-d. In the Christian bible (2 Corinthians 4:3-4), Satan is called the god of this world. However, in Judaism Satan is an agent of G-d, created by G-d for a specific purpose, and something very good. Satan is simply an agent of G-d, just as all the other angels are simply agents of G-d. This is why we frequently see passages where the author appears to interchange G-d and an angel (leading to the often erroneous Christian concept of a christophony).
If we take a look at Isaiah 45:7, we see that Hashem is the creator of everything, as the text says, bringing forth light and create darkness, I make peace and create evil, I am G-d who does all these things. In the Jewish bible, everything is under the jurisdiction of G-d and under His power all forces, even evil forces. Everything comes from G-d, He created everything, good and evil. That being the case, Satan is not a rival of G-d, he is a messenger of G-d and unable to do anything outside of G-ds will.
