On Shavuot Eve, Rabbi Shimon Bar Yochai, may he rest in peace, and his colleagues, who were an exemplification of God's study in heaven, would study the midrashic and mystical interpretations of Torah, Prophets and Writings, the mysteries of PARDE"S, to prepare for the bride… Know that they had songs and melodies based on Wisdom and mysticism (sod), which they would sing to cheer the heart and to adhere to the upper world, and to draw plentitude and heavenly mercy through melody, through the concealed meaning of "As the musician played, the spirit of the LORD came upon him". This is our custom as well, and on the first night of Shavuot, we sing the 32 piyuttim (32 is the numerical equivalent of lev, which means 'heart', in Hebrew] which have been imparted to us by Wisdom.