This love will rise from the depths of the heart, that is, from the right ventricle — the seat of the divine soul’s emotional faculties, it would be filled to overflowing — i.e., the love would overflow into the left part of the heart, to affect the emotional faculties of the animal soul which reside there. To crush the sitra achra; specifically, the element of Water in the animal soul, which gives rise to lust for physical pleasures.
The effect of the divine soul on the animal soul’s element of Water would be to change and transform it from a lust for mundane pleasures to a love of Hashem.
As it is written,’בכל לבבך’ — which our Sages interpret ‘בשני יצריך’, with your good inclination and also with your evil inclination.” Accordingly, the evil inclination must also come to love Hashem.
This transformation of the animal soul’s lust to a love of Hashem entails rising to attain to the level of abundant love, a love surpassing even the level of the “powerful love, like fiery flashes” that was mentioned earlier. This level of love is what Scripture describes as a love of delights; it is the experience of delight in G‑dliness that is a foretaste of the World to Come, since man’s reward in the World to Come consists of delighting in G‑dliness.
(Lessons in Tanya Chapter 9)