Humans respond best to love and compassion. Why? Because it's the essence of the Universe.
Deep down, every creature wants to be loved and cherish. Even cockroaches. Every other living and non-living being on this planet is the product of same evolutionary forces that 4.3 billion years later have lead to us. All of us.
Who are we to determine who is worthy or not of love and kindess? As the old saying goes, kindness and compassion are free, yet they give so much, not only to the receiver, but to the giver as well, since it has been shown in study after study that happy humans are healthy humans.
Closely linked to compassion is gratitude