Spices at Havdala
At havdala at the close of Shabbat the custom is to make a blessing on pleasant fragrances. Early authorities mentioned two reasons for this custom:
 Shabbat, the fires of hell are extinguished. Even the sinners get a reprieve from their punishment one day a week. As Shabbat goes out, the flames are fanned again, and begin to burn and create a stench. The smell of the spices masks the stench of the fires of hell.
 On Shabbat we get a "neshama yeteira", an extra soul. As Shabbat departs, so does this extra spirit. In order to console ourselves on the loss of this special level of spirituality, we smell pleasant fragrances, which have the ability to "restore the soul" (Bach OC 287, based on Tosafot Beitza 33b "ki havinan").
Two weeks ago, we cited an aggada which suggests that the flames of hell are fed by the passions of the wicked.
When we face the light of truth in the World of Truth which follows this life, our misdirected passions torment us mercilessly. Yet on Shabbat these fires are restrained.
Perhaps this is a hint that on Shabbat, when we are actually commanded to indulge in bodily enjoyments, we have a special ability to use our passions in a positive, holy way; on this day they cease tormenting us (see also Pesachim 54a).
Of course, most of us do not notice any particular bad smell emanating from the nether world on Saturday nights. The stench of Gehennom is something we sense on a very inner, instinctive level - befitting the sense of smell, which corresponds to an inner, direct apprehension of the nature of an object (as explained in the column for parshat Ki Tisa 5761).
This is closely related to what we explained last week, that Shabbat is not only a day when we refrain from material repair, it is also a day when we have a partial respite from even spiritual repair. As we confront hard moral choices and troubling moral ambiguity at the start of the new week, we become acutely aware deep inside of us of the presence of rottenness in the world. This could be likened to the stench of the fires of hell. We console ourselves with beautiful smells, which are the "enjoyment of the soul". We remember the many brave and righteous acts which are also performed, and the immense human capacity for good.
This is equally related to the loss of the "neshama yeteira". This neshama elevates us above the level of petty evil, but as we descend back into mundane concerns we are troubled by the presence of moral rottenness; again, fragrant smells remind us that even within the world of materiality there is enjoyment for the soul.