He answers that on hearing the laws of Kashering, they drew a practical inference for themselves; If even a weak taste of Treif that is absorbed in non-kosher vessels requires Kashering, then surely their thoughts of sin need cleansing too.
Our bodies are a like a vessel. They may be used for “Kosher” - to carry out the desires of our G-dly soul in service of Hashem. But we may also use our bodies for “Treif”; to follow the desires and whims of our evil inclination and animalistic desires.
When a person sins, even if only in speech or thought, the effects of negativity permeate their being. To restore our purity, we need to undergo a spiritual Kashering. This cannot be done in a superficial manner. Rather, like the Kashering of vessels one must reach into the depths to extricate all traces of the Issur.
The basic principle in Kashering is referred to as K’Bolo Kach Polto - the way in which the Issur was absorbed is the same way that it must be extracted. The Torah teaches this with the words ‘whatever is used in fire you shall pass through fire and then it will be clean’. This gives rise to the various Kashering methods that range from exposure to fire until the vessel glows red hot, to merely washing the vessel if it was only used for cold foods.
In addition to Kashering the vessel must be immersed in a Mikva to give it the Kedusha (holiness) befitting a Jewish utensil.
Spiritual Kashering follows the same principles. We must drive out our negativity with the same intensity with which we sinned. We do this by infusing our souls with the flames of love for Hashem and passion in our observance of Torah and Mitzvos.
After “Kashering”, we must then immerse ourselves in the purifying waters of the study of Torah, to imbue our lives with the holiness and purity, so that we can be Kosher receptacles to receive the revelation of the Divine presence that rests within our souls.
