Human Nature

I - Both body ("guf") and soul ("nefesh" or "neshamah") are morally neutral.

Jews believe that we, human beings, are body* and soul in equal measure and that neither body nor soul is sinful. We can choose to use our bodies for positive (in a loving, caring, life-affirming way), or for negative (in a way that hurts, destroys, oppresses) purposes.
We have many ethical teachings around choices one can make with body and soul in order to help us take the life-affirming road.

*(Even when one is dead, the body must be treated with utmost respect and care. Our bodies are not simply useless shells.)

II - Human beings are not sinful: we are torn throughout our lives between two sides of our natures.

Each of us has a yetzer ha-ra (lit.: "a bad side") and a yetzer tov (lit.: "a good side"). We may pull toward either one at different times - sometimes acting with compassion, caring and cooperation and at other times acting more selfishly or destructively. The yetzer ha-ra is not even always bad -- sometimes our selfish impulses lead us to do things that contribute positively to the well-being of others.  People are neither perfect nor suffused with sin.  Much of the time our words and actions don't fit any real "black or white" categorization.  We each make a variety of choices and strive to tilt the scale toward the positive -- that which enhances our world and those around us -- most of the time.

III - Second chances are possible

Jews embrace the concept of teshuvah (return).  Everyone has the capacity to change and grow over time: to return to the Godly soul that resides within each of us.  Past choices or mistakes need not define us for a lifetime.  No matter what we have done or said in the past, we can choose better patterns of behavior and more thoughtful words in the present.  Life isn't about perfection - it's about using our experience to continually develop our characters.