The essence of love and compassion is understanding, the ability to recognize the physical, material, and psychological suffering of others, to put ourselves "inside the skin" of the other.  We "go inside" their body, feelings, and mental formations, and witness for ourselves their suffering.  Shallow observation as an outsider is not enough to see their suffering.  We must become one with the subject of our observation.  When we are in contact with another's suffering, a feeling of compassion is born in us. Compassion means, literally, "to suffer with."