This week's portion is called Vayikra, "And He called," the first portion of the third book of the Torah. The order of events leading up to this parashah (and the book as a whole) is that, following the construction of the Mishkan, the Sanctuary of the Jewish people, at the end of the previous book, God teaches us the laws pertaining to it, beginning with sacrifices in all their forms and at all times, and continuing with the laws of purity and impurity, kashrut, and other precepts related to the Sanctuary.
The custom is that the first thing studied with a child is precisely the Book of Leviticus. Its first parashah deals entirely with animal and plant offerings that were to be brought to the Mishkan, either voluntarily or by obligation. It is, in essence, a highly technical parashah, describing in great detail the parts of the animals and plants to be burned on the altar, how the blood was to be offered, what types of sacrifices existed, and so on. The question is, why study this with a child? Given that the Torah contains so many significant stories that shape morals and values, why study something so technical?
The answer lies in an expression repeated several times in the parashah (Leviticus 1:9, 1:13, 1:17 and beyond): "A pleasing aroma, an offering to God." This expression refers to the fact that a sacrifice offered in the manner described in the Torah becomes, when burned on the altar, "a pleasing aroma […] to God." Our sages ask, does God have a nose to smell a pleasing aroma? Furthermore, part of what was burned were the feathers of doves, which produce a very unpleasant odor for humans. What is "pleasing aroma" about this?
Our sages explain this using a play on words in Hebrew, that the "pleasing aroma" is, in reality, a pleasure to God, which He dictated and we fulfill (see Rashi on Vayikra 1:9) (in Hebrew, reaj nijoaj it transforms into najat ruaj), that is, despite being something incomprehensible to man, the very fact of having fulfilled a Divine order generates satisfaction and pleasure in God.
Returning to the point that this is the first thing a child studies, the idea is that the Torah is not just a book of good qualities, morals, and ethics, along with a lot of interesting stories, but rather a book that describes God's will, what God wants from each of us, regardless of whether we see its usefulness or meaning in it. And herein lies the highest level of Torah observance, when a person performs a mitzvah simply for what it is: a divine commandment.