Rambam on Mishna Peah 1:1

And concerning what they say, "one gets the interest [literally eats the fruit] and the principle [literally the horn] remains to him ", it is to tell you about this: all the commandments can be divided into two groups, one group that especially apply between a person and the Eternal, such as tzitzit, tefillin, Shabbat and idol worship, and one group that apply to the regulating of human relations, such the prohibition against theft, deceit, hate, bearing a grudge, and the commandments to love one another, and not to lie to one another, and that one of us should not stand by another being damaged, and to honor parents and scholars who are the parents of all. If someone upholds the commandments between oneself and the Creator there is a reward given to him for this in the world to come as is illuminated in perek helek [the tenth chapter of Sanhedrin]. And if a person upholds the mitzvot that apply to the regulating of human relations there is a reward in the world to come because he upheld the mitzvah, and he obtains benefit in this world through behaving well with people, for if he acts in this way, then the other person will act in this way, and he will get the same benefit. All the mitzvot between people are included in the general category of acts of loving kindness. Behold you will see that Hillel the Sage when a non-Jew asked him, "teach me the Torah on one foot", he said to him, "that which is hateful to you do not do to your fellow", and when you research this you will find that the study of Torah is weighed against them all because in the study of Torah a person knows all this, as they are illustrated to us, and study brings us to act.