From Rav Yosef Stern’s Sfas Emes sefer, Days of Joy:


There’s a halacha in germara Shabbos 21b that describes how certain oils and wick are “not acceptable for Shabbos candelabra, but are permitted for the Chanuka Menorah.  The substances are prohibited for Shabbos use because of the flame’s inability to cling to the wick.  Likewise, the light of Torah is unable to fully penetrate certain souls even on Shabbos.  Yet on Chanuka these rejected wicks may be used.  So too, souls that are not inspired by the weekly Shabbos are spiritually moved by the yearly observance of Chanukah. A certain spark, an inner purity, always remains burning bright in the heart of every Jew.  This spark, know as the Nekudah HaPinimius, constrained all year long from permeating the Jewish psyche, is liberated on Chanukah through the power of praise and gratitude, for the miracles that occurred at this time”