This week's Torah portion tells us to "Love your fellow as yourself."
The Talmud relates the story of the budding convert who came to the venerable sage, Hillel, and asked him to teach him the whole Torah whilst standing on one foot. Hillel replied: "What is hateful to you, do not do to your fellow. This is the whole Torah--the rest is commentary..."
Rabbi Akiva considered love for one's fellow "a vital principle of the Torah."
Why did Hillel place so much emphasis on this particular precept? We can understand how it underlies those commandments which apply between our fellow man; but how does it impact on those commandments which apply between mankind and G-d? How is brotherly love related to keeping the Sabbath, or Kosher?
We need to look further into the concept of loving one's fellow "as oneself." How can I love someone else like myself? Ultimately, no matter how close we may become, do we not remain distinct individuals? Do not "self" and "other" forever remain two separate and unbridgeable entities?
This is true when we consider our physical existence. As physical beings, self and other are indeed two distinct entities. In the spiritual realm, however, they are ultimately one, for all souls derive from the same source, united with G-d at that source.
When we regard our physical selves as the "I" and the soul as a mere accessory, we are indeed different from another. If, however, we regard the soul as the "I", our spiritual needs as paramount, then the differences between us dissipate and we are able to love another just as we love ourselves.
Loving another person the same way as one loves oneself involves acknowledging and nurturing our own spiritual roots, seeing and relating to our deepest self.
And that is the underlying principle behind every mitzvah.