The Rebbe says:
1. As a preparation to the upcoming inauguration of the Mishkan (the Tabernacle) which begins in next week’s Torah portion (Parshas Tzav) and continues through the portion after that (Parshas Shemini), this week’s Torah portion talks all about the various offerings.
2. The order in which the Torah decides to tell us about the offerings is first to discuss the offerings which were voluntary offerings, such as the Burnt Offering (Korban Olah), the Meal Offering (Korban Mincha), and the Peace Offering (Korban Shelamim), and then to tell us about the obligatory offerings, such as the Sin Offering (Korban Chatas), and the Guilt Offering (Korban Asham).
3. The Rebbe now questions this order of instructions:
Wouldn’t it make more sense for the Torah to teach us first about the offerings which are obligatory and only then tell us about the voluntary offerings? After all, if a Jew didn’t want to bring a voluntary offering he didn’t need to know the laws concerning them, however every Jew needed to bring an obligatory offering and therefore needed to know the laws concerning them!