In the spiritual spheres there is a source for each of the four spiritual elements: Fire, Water, Wind and earth. Everything in this world is made up of varying quantities of the four spiritual elements and the physical manifestation of the combination of those spiritual elements expresses itself in a revealed sense thus we can sometimes discern when there is an unbalanced ratio of the four spiritual elements. i.e. in our drinking water there is a high concentration of the spiritual element of water although there are also other elements thus we see the build up of scale inside a kettle which is from the earth element within the water. Passion and desire among other traits are sourced primarily in the spiritual element source of fire.
And even if yesterday one succeeded in overpowering one’s evil inclination the next day their evil inclination is back in full force and needs to be subdued once again. Although there are ways of getting rid of one’s evil inclination as the Alter Rebbe quotes Dovid Hamelech who describes his hollow void to which our Sages tell us that Dovid Hamelech killed his evil inclination through fasting, this is a long and difficult journey and not expected of everyone, but what is expected that each and every one of us can control and subdue our evil inclination and through continuously controlling and subduing he will remain at bay.
