In this week's Torah portion, Shlach (Sends) tells us (among other things) about the mitzvah of challah. When a person prepares dough with a certain amount of flour from one of the five grains (wheat, barley, rye, oats, spelt), they must set aside a portion that, in Temple times, was given to the Kohanim (priests). Today, even though we don't have a Temple, we also set aside a small portion, which we later burn.
Every matter in life can be viewed from different perspectives, and as the Baal Shem Tov said, one should learn some lesson from everything one hears or sees in service to God. This is especially true of a Torah commandment, whose purpose is to be a hora—a teaching—for life, and whose commandments can and should be understood on different levels.
The most basic level is that of observance, where there is a Divine Will (independent of the "why" of that will) that comes down to man as a practical command: when you prepare a dough, set aside a portion for the Cohen.
Then there are the reasonings, where we find three general levels: 1) a hidden reasoning, known only to God, 2) a reasoning revealed by God in His Torah, and 3) a reasoning deduced or "found" and revealed by man.
It is important to keep in mind that we can never reach the depths of Divine thought simply because we are limited creatures and He is the Infinite Creator, which paradoxically leads us to understand that we cannot understand God... even the reasonings revealed by God are not the true reason behind the Mitzvah, but are only a tiny comprehensible portion of something that totally surpasses human beings.
With this in mind, a simple analysis of the Mitzvah of Challah leads us to think that since the Kohanim did not own land and spent much of their time serving in the Temple or other specific tasks of service to God, they had neither produce from their own fields nor money to acquire other people's products. Therefore, the Torah commands whoever prepares dough to give a portion of it to the Kohen so that he has something to eat (in addition to other donations, such as Terumah, Reshit HaGez, etc.).
However, a deeper analysis reveals a practical lesson even for those not preparing dough. The verse from which we learn this mitzvah says (Numbers 15:21), "From the first of your dough offerings, give an offering to the Lord for all generations." The Hebrew word for dough is arisotechem, which can also be translated as derived from the word arisha—cradle or bed. According to this new reading, the verse would be telling us, "From the first of your beds," meaning that as soon as you get out of bed each morning, "give an offering to the Lord for all generations.""
The mitzvah of challah teaches us that we should dedicate the first and best moments of the day to God, giving them, so to speak, to Him.
Each person should set aside a moment at the beginning of the day to thank God for the very fact of being alive, to focus on what the spiritual work of the day should be—that is, what should be accomplished that day and how it should be filled with holiness. Otherwise, how can we know that our day wasn't wasted?