Tales and Maxims from the Midrash oleh Samuel Rapaport

JUST as the Written Law given by Moses emanates from God, whilst He Himself only proclaimed the first two commandments of the Decalogue, owing to the Israelites being too terrified to hear Gods voice (Deut. 20. 19), and the whole of the Torah was then conveyed to Israel by Moses, so he likewise received the Oral law, which he was not allowed to commit to writing. This Oral law had to be taught by word of mouth side by side with the Written law, and thus the former became an unfolding and sequel to the latter.