Chasidut for Pesachim 107:23

This corresponds to "elimination of leaven is only by burning" (Pesachim 5b). For, "they emerged from fire and fire will consume them". (Ezekiel 15:7). Providence in nature corresponds to day and night, light and darkness, as said, and also corresponds to luminaries of light and luminaries fire. Luminaries of fire dominate when the luminaries of light disappear, which is at night and in darkness. For, 'they emerged from fire and fire will consume them'. Ezekiel 15:7. Providence in nature corresponds to day and night, light and darkness, as said, and also corresponds to luminaries of light and luminaries of fire. Luminaries of fire dominate when the luminaries of light disappear, which is at night and in darkness. See LM I 67. Fire corresponds to the intensity of judgment that is drawn from nature, which is why G-d created fire after the Sabbath, through Adam, as our sages said (Pesachim 54a). This alludes to nature, in that providence disappeared. Nature corresponds to (Deuteronomy 8:17), "my power and the make of my hand have accomplished", like fire, which was created by a human act. Therefore nature is most strongly attached to fire, which represents the intensity of judgment. And therefore we recite the havdalah after Shabbat over fire. Because this is the essence of differentiation and separation. The power of the tree of knowledge of good and evil is mainly from the power of nature, which corresponds to fire, and by our reciting the havdalah over fire, we thereby separate the good and subdue the bad that is attached to the fire as nature, and then the fire itself is transformed into holy nature. For the truth is that even nature is Providence, since G-d himself guides nature as He wills, and when we believe and know that everything is Providence, and even nature becomes Providence, and then even fire is sacred. This is represented in 'who creates the luminaries a fire', which we recite after the Sabbath during havdalah, declaring that we believe everything to be from G-d and that fire is an aspect of the nature that G-d himself created, for nature is Providence. Then, everything is sacred, representing the rectification of the tree of knowledge of good and evil. Specifically through this, evil falls away, as in, 'they emerged from fire and fire will consume them', for its main power is from fire, from nature, and when it becomes evident that even fire, nature, is also from G-d this itself subdues it. This corresponds to burning leaven with fire, for divine providence has been revealed, and then we know that everything is from G-d, and that even nature, represented by fire, was created by G-d alone. Then leaven, representing natural sciences, corresponding to the power of the nations, is subdued and eliminated specifically by its own source, by fire, for 'they emerge from fire and fire will consume them'.