One should see the world, and see himself as a scale with an equal balance of good and evil. When he does one good deed the scale is tipped to the good - he and the world is saved. When he does one evil deed the scale is tipped to the bad - he and the world is destroyed.
MaimonidesWHEN reading my present treatise, bear in mind that by "faith" we do not understand merely that which is uttered with the lips, but also that which is apprehended by the soul, the conviction that the object [of belief] is exactly as it is apprehended. If, as regards real or supposed truths, you content yourself with giving utterance to them in words, without apprehending them or believing in them, especially if you do not seek real truth, you have a very easy task as, in fact, you will find many ignorant people professing articles of faith without connecting any idea with them.
Maimonides