The movement of subtle-ization of gross energy is the transformation of love.
This does not happen from outside. But it is a transformation initiated within the gross energy itself – to subtle-ize itself – to love itself. And this endogenous energy of subtle-ization frees the gross energy AND the gross energy thereby utilizes its own potential of subtle-ization to free itself.
To give an analogy to reduce the abstractness, every cell, every part, every atom, or every unit of experience has the capacity to love itself, or subtle-ize itself. The energy for love does not come from outside, that is an illusion. The energy coming from outside can make inspire you, make it easier, serve as an example for you to initiate that process within your OWN experience. Ultimately, the outside energy simply REMINDS YOU, evokes or inspires that part of YOU, your endogenous potential energy, for subtle-ization or loving the entities of your own experience.
Everything happens by itself, even the process/alchemy of love which frees the gross to the subtle happens from love (or subtle-ization force).
Another analogy for understanding subtleization would be – Heat a metal ball –> it becomes liquid –> Heat the liquid –> It becomes gas. So the gas is the freed subtle-ized version of the gross which was the metal ball.
In this case, the koshas concept can be used to demonstrate this process:
Journey to the Abstract 