"My ally is the Force, and a powerful ally it is."
Yoda

"May the Force be with you."
Jedi well-wishing phrase

The Jedi were unified by their study of the Force: an "energy field" that emanated from every living thing. The Jedi sought to understand the Force so that they could use its power to protect and aid the people that they served. The Jedi believed that the Force could be harnessed through careful study and contemplation to benefit the user and the world around them. As they studied the light side of the Force, the Jedi encouraged their members only to use the Force for healing and defense?never in anger or fear. Unfortunately, several of the Jedi order throughout history disagreed with this view, arguing that other, darker uses of the Force should be allowed. This disagreement was one of the main issues the Jedi faced in their constant battle with the Sith.

"A Jedi's strength flows from the Force. But beware the dark side. Anger, fear, aggression. The dark side of the Force are they. Easily they flow, quick to join you in a fight."
?Yoda

The dark side of the Force brought with it a great temptation for many Jedi; to many the dark side seemed a quicker and easier path. Pursuit of the dark side, however, was a self-destructive endeavor, and many Jedi who tasted dark powers found it harder and harder to turn away. Though some Jedi could be redeemed back to the path of the light, many fell and became Dark Jedi, some of whom were members of the Sith Order. Further, the pall of the dark side could diminish Jedi ability, clouding their insights into important matters. For these reasons, practice of dark Force powers was expressly forbidden by the Jedi Council. Those fallen to the dark side, however, the Jedi tried to save. To the Jedi, killing was a last resort. This quality was at once a strength and a weakness of the Order.