When considering the word compassion, the word caring might be the first word that comes to mind, or it would most certainly be included in a definition.
Caring is an emotional state. In fact, it is perhaps our strongest emotional state. Being an emotional state makes it an egoic state, however, which makes it one of our strongest fixations to our three dimensional reality.
We do things in life because we care. We care about our causes, our ambitions and our positioning among other egos, e.g. self esteem.
Compassion is non-egoic. It is the higher form of caring that has shed any attachment to the causes, ambitions and self-esteem that caring is concerned about.
Caring has a dual nature to it that places it in the realm of judging. If you fall on the side of a cause you care about, it is perplexing to you that those, who don't see it as you do, just don't care. And they may be equally perplexed that you do care.
Compassion has no such duality and therefore is never entangled in the rightness or wrongness of a particular cause or object of caring. It is the cause of action for someone who has completely lost egoic definition for their life, and lives in absolute humility.
It consumes no physical energy as the act of caring gets consumed in worry, fear, hate and other mentally and physically depleting emotional states. The emotional states manifest themselves when our caring is connected to outward things (all things are outward)over which we have no control.
We often see people taking up great causes because they care deeply. We also see these same people "burning out" when the cause is daunting and the outcome is not manifesting as they believed it should.
Caring drives us to burn through our energy because of its inherent connection to outside causes.
Compassion is free from outside connection because ego is not involved. Motivation changes from passion and pursuit to simply will.
Not being connected to egoic outcomes, we never loose energy because of worry, fear or other emotional states as we no longer are concerned about success or failure.
It is an act of gods and since we are gods, we need to decouple our caring, our ego and things we tend to be passionate about from our natures and live as the gods do - by will only.
In so doing, no energy will be lost to unseen things we have no control over, but will be ours to use as the gods do.