Should the father not teach the child, the grown child must study, because the verse links learning to performance—how can one properly keep the Torah without studying it? Nor does the obligation end, as a verse in this week’s portion, 4;9, warns us against letting the words of Torah leave our hearts all the days of our lives, and without constant study, we forget.
Neither poverty nor wealth excuse the failure to study. God’s order to Yehoshu’a to think of Torah day and night led to the assumption we are all supposed to set times for study in the morning and at night, and our ultimate judgment starts with the question of whether we were sufficiently involved in study. Later in the mitzvah, he throws in Hillel’s warning from Pirke Avot to reject the temptation to say, “I’ll learn when I find the time,” because one might not find the time [my Rosh Yeshiva, R. Aharon Lichtenstein, zt”l, used to say, will definitely not find the time]. Unless we make sure to set up our lives that way.
Kiddushin 30a also tells us to divide our study time into three equal parts, Mikra, Mishna, and Talmud, despite the basic mitzvah referring only to Written Torah. Those three terms likely mean (Rashi, Rambam, and Sefer HaChinukh have very similar definitions) the Written Torah (for Rambam, all Tanakh), the Oral Law [my teacher Prof. Twersky, zt”l, pointed out that Rambam seems to have considered all the Torah ideas propounded up until a persons’ time among the Oral Law; for him, for example, Geonic works were Torah She-be’al Peh], with Talmud being to develop a full, deeper understanding of those laws [with nuances about what “deeper” means].
