As Einstein's beautiful words written to a grieving parent points out, life cannot fully be appreciated or understood without "widening our circles of compassion." The basic message of most religions and spiritual movements is that a more fulfilling and functional life cannot be had without the understanding that compassion has to be the ground of our thoughts, words, and deeds.
So why is compassion so important?
Compassion is not important because I said, or the Pope said, or even God said that it is important. Instead, the reason compassion is important is because that it leads to a greater happiness and a healthier body, mind, and spirit for all. Compassion is truth in action.
The truth is that we are not separate in any way. That we can only understand something, anything, from its relation to something else. Life cannot exist without relationships and therefore life is not separate. As Einstein points out we are an inseparable part of the universe. When we act outside of compassion, as if we were separate, then we feel disjointed, unbalanced, out of touch, and many times terribly unhappy.
Compassion captures the essence of the truth of our relatedness. When you think, feel, or act in accordance with the truth of existence then you are acting in compassion. When you are acting in compassion you are seeking to benefit the various aspects of existence, including but not limited to yourself.
Love captures the essence of life because it always must include the other. In fact, as Einstein relates, the human being is" a part of the whole" and when we are not in this understanding then we are in "a kind of prison for us, restricting us to our personal desires." When we understand the truth of our existence then we know that we have to broaden our focus to include the caring and consideration of the other.
So we believe that we can build up our self concept with this or that magical formula or this or that appeal to authority but in reality we need to break the illusion of an independent self for a healthier and happier life. There is no independent self just relationships existing in some sort of temporary structure or movement. When we break this "delusion" of an independent self that exists outside of the whole then we break out of "a kind of a prison for us."
Compassion allows us to take the focus off of this delusion of self and it opens us up to the wholeness that is the reality of life. Love is the royal road to a better world and a better life precisely because it is operates from the truth.