Because if a person does not recognize who is the One who gave Torah to that person, and what the person is supposed to observe, how would the person fear and observe the mitzvot? And regarding this the rabbis said: an ignorant cannot be pious, and a boor cannot fear sin (Avot 2:5).

Another Introduction to Tiqqunei ha-Zohar For Rosh Ḥodesh Elul, Day 1