הלכות דם א
(Painting by Yitzchak Moully)
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.