How can love exist between two human beings? Baal HaSulam explains that for this to happen people have to be similar in their properties. The universal law is effect in the entire Universe, in all the worlds, including ours; it is called the law of equivalence of form. According to this law, I sense, perceive, and comprehend only the things that are common between me and the object that I investigate, perceive, and observe. If no common property exists between a certain object and me, I am unable to sense it. If there is no commonality in thought – at least, minimal or partial – between another human being and me, I am unable to understand him or her.
But if two egoists do love each other, how is it possible? In such a case, they have to resemble each other in their properties. I have to love whatever the other person loves, to hate whatever the other person hates, and this how we will connected with each other. It follows that we are not talking about love between the two. We are talking about their equivalence of from, resemblance in desires and thoughts, an additional aspect that can be measured. I can compare my desires and thoughts to those of another person, and the measure of their resemblance will determine the connection between us.
Courtesy of http://www.youtube.com/watch?v=GMqSKJYMZww