Pirkei Avot, 1:2

"Shimon the Righteous was of the last survivors of the Men of the Great Assembly. He used to say, the world is based upon three things: on Torah, on service [of G-d], and on acts of kindness."

As one of the last survivors of the men of the Great Assembly, Shimon the Righteous must have felt the obligation to transmit the essence of Torah to the next generation in the most understandable fashion, so that it would continue.  The first two of the three things are not surprising: the Torah is the thing that Shimon was obligated to transmit, as one of the last survivors of the last group to whom it had been passed from Moses, who received it from God.  The Torah had to be the first thing that Shimon would say the world stood on.  It is also not surprising that service of God would be the second thing, for the service of God, through the performance of the Mitzvot, is what the Torah commands.  What is surprising is the third thing: acts of kindness.  It doesn't follow the pattern.  The logical next thing, after service of God, which is following the commandments of the Torah governing the relationship between man and God, would be following the commandments of the Torah governing the relationship between man and man.  Acts of kindness depart from the pattern of following the commandments of the Torah, in favor of a generalized human-centered observance.  Note that that third thing is not "service of man," which would parallel service of God; rather it is acts of kindness, which are defined by human feelings about what constitutes "kindness".  This is an example of an essential inclination of rabbinic Judaism, similar to the tendency of the oral tradition to favor leniency in interpretation of harsh Toraitic punishments, and dissimilar to the tendency of the Moslem tradition toward literal interpretation of harsh Koranic punishments.  It is also similar to the teaching of the Golden Rule (don't do to others what is hateful to you) and forshadows the tendency of liberal Judaism to view the essence of Judaism as tikkun olam, which is generally interpreted to mean doing good deeds for other people, both of which ignore the God-centered commandments.  Shimon the Righteous had it as one of three things upon which the world stands.  In modern liberal Judaism, the third leg has become longer than the first two.  This is not meant as an indictment of the inclination to human kindness as a direction of Jewish observance; rather, it is meant as an observation about how the tradition has developed.