Ultimately, the reason why love and compassion bring the greatest happiness is simply that our nature cherishes them above all else. The need for love lies at the very foundation of human existence.
True happiness comes from having a sense of inner peace and contentment, which in turn must be achieved by cultivating altruism, love and compassion, and by eliminating anger, selfishness and greed.
According
to my own experience, the highest level of inner calm comes from the
development of love and compassion. The more concerned we are with the
happiness of others, the more we increase our own well-being.
Friendliness and warmth towards others allow us to relax and help us to
dispel any sense of fear or insecurity so we can overcome whatever
obstacles we face.
'Thou shalt not kill' does not apply to murder of one's own kind only, but to all living beings and this commandment was inscribed in the human breast long before it was proclaimed from Sinai.
Can you imagine if you really let it in that you are not a problem to be solved in any way? Imagine you knew that anything that would tell you otherwise is just a movement of thought in the mind that says "Whatever is, isn't the way it is supposed to be." So the biggest act of compassion starts within. And when the self is no longer seen as a problem, this is called "the peace that passes all understanding."
From the Sun I learned this: when he goes down, overrich; he pours gold into the sea out of inexhaustible riches, so that even the poorest fisherman still rows with golden oars. For this I once saw and I did not tire of my tears as I watched it.