The primary means through which Torah is revealed is through kindness, love, desire, and yearning for Hashem. Through these things one is able to create the vowel points and the forms of the letters of the Torah. Prior to Kabalas HaTorah the main avodah of the tzaddikim was to desire and long for Hashem. This was until Avraham Avinu, who was the leader of the faithful and the circumcised, came and achieved what other tzaddikim were unable to. The notion of yearning and desire correspond to the traits of kindness and love, which are the traits of Avraham Avinu. From that point on [once Avraham perfected these traits] many Torah concepts were brought forth into the world, and the rest of the Avos, the Shvatim, and their sons were able to engage in Torah study. This continued until Moshe Rabbeinu and all the Jews of that generation (who were all tzaddikim) came. And, with their yearning and desire for Hashem were they able to create the different forms of the letters of the Torah. Through the work of that particular generation were they able to achieve Kabalas HaTorah.