Why Command Aaron and his sons?
In most years, Parshas Tzav is read in close proximity to Pesach, the Season of our Liberation. There must therefore be a thematic connection from this Parsha to Pesach.
The parsha begins with G‑d telling Moses to “Command  Aaron and his sons “ concerning the Olah-burnt offering sacrifice. “It is the olah-offering that stays  on the flame, on the Altar, all night  until the morning…”
Rashi comments on the unusual word “command” anticipating the question why the Torah uses this word instead of the more common words such as “speak” or “say.”
Rashi’s answer is that this particular command concerning the burnt offering poses a challenge and the Torah needed to make sure that the people meet this challenge. Thus the use of the stronger term “command.”
Rashi proceeds to cite a difference of opinion by our Talmudic Sages as to what is the primary challenge that necessitated commanding them to comply.
The first opinion is that “the term ‘command’ can only be meant to express urging on for the immediate moment and for future generations.”  Rabbi Shimon added: “Scripture must especially urge in a situation where there is a loss of money.”
The anonymous rabbis believe that the command was needed to underscore the urgency to fulfill this offering for the immediate moment as well as for the future. These Sages focus on a dual challenge that confronted to Kohanim. First, to transmit this commandment concerning the Olah to the Kohanim that they implement G‑d’s will without delay. And a second challenge was to transmit this command to their children.
Why was there a greater challenge here, as opposed to all the other commandments which were not addressed with the word “command?”
The answer lies in the nature of the burnt offering. It is the one offering in which one sacrifices the entire offering. By contrast, other offerings provided some benefits to the Kohain who performed the service in the Temple. The burnt offering was totally consumed on the altar, hence the reluctance of some Kohanim to bring such offerings.
But, the question can be asked, what is the basis for the reluctance. If it is due to the monetary loss incurred by the one who brings the offering, that concern was voiced by Rabbi Shimon. The anonymous view of the Sages seem to think that there was a challenge distinct from the monetary one.
Second, why are the Sages more concerned about future generations than Rabbi Shimon?
Quid-Pro-Quo and Our Youth
The answer to these two questions lies in the human frailty that limits one’s time, effort and money to situations where there is a tangible benefit in return. Living in a world of commerce, the name of the game is quid-pro-quo. We give and expect something in return.  
We might even be prepared to make major financial concessions as long as we are guaranteed to profit from that investment in the future.
Thus, the Sages tell us that the reason for the special command here with respect to the burnt offering is due to the fact that there is no return; the entire offering is burnt on the altar. A person who is asked to make this sacrifice is going against human nature and will tend to procrastinate. Thus the Torah exhorts him to carry out this command without delay.
This challenge is further exacerbated when we try to impart the need for unrequited sacrifices to the next generation; to our youth.
The nature of many of our youth is to pursue a path in life that eschews sacrifice. The young are constantly asking “What is in it for me/us?” There must be a quid-pro-quo. They will argue, “If you expect me to give of my time money and effort, what do I get out of it?
Indeed, there was always a schism between generations; a “generation gap.” The new generation sees itself as “modern,” more in touch with the changing realities and views their parents and elders as an anachronism, and their values irrelevant.
Thus the Sages feel that there was a special need to exhort and command transmission of the value of sacrifice to the next generation.
The Test of Affluence and Poverty
The challenge of passing on sacrifice is most pronounced in periods of affluence, when we are accustomed to having all of our needs and wants provided for. In times of wealth, many parents tend to spoil their children, supplying them with all of the delicacies, toys, games and pleasurable experiences. As a result of the abundance of material good in their upbringing the children are programmed to expect only things and experiences that are painless. They are not accustomed to suffering or even mild discomfort. The prospects of lacking the provision of their needs and wants will prove to be painful.
The first opinion of the Sages maintain that the greatest challenge for sacrifice for G‑d or others is the test of wealth. And living in affluence is particularly challenging to our youth when they are called on to make sacrifices.
Rabbi Shimon, on the other hand, is concerned about the monetary challenge that could deter the Kohain from carrying out his responsibility to offer the burnt offering. In his opinion, the greater challenge is the test of poverty.
An Ancient Debate
These two opinions seem to be arguing about an age old question, which of the two is a greater test; affluence or poverty.
This dispute did not begin with the command to bring a burnt offering; it is an underlying theme in the saga of the Jewish people as they were liberated from Egyptian bondage and poverty and thrust into a state of affluence when they emerged with the wealth of Egypt.
To be sure, both took a toll on the Jewish nation. The suffering of the Jews in Egypt crushed their spirit, whereas the wealth that they acquired during the Exodus was implicated in their construction of the Golden Calf.
Experiencing Wealth and Poverty in the Haggadah
Indeed, in the Passover Haggadah we will be referring to both the test of poverty and wealth. The suggestion here is that both can be features of Galus from which we need to be liberated.
Before reciting the Haggadah we recite Kiddush over a cup of wine, one of four we will be drinking at the Seder that symbolize the four expressions of freedom. And while we drink these cups of wine (as well as when we eat the Matzah) we recline, the way the ancient aristocrats would eat their meals, as a further symbol and expression of freedom and affluence;
And then we begin with the recitation of the Haggadah which highlights the state of poverty:
“This is the bread of affliction our fathers ate in the land of Egypt.”
This is followed by breaking the middle Matzah, so that the Haggadah is recited over a broken piece of Matzah; a symbol of poverty, inasmuch as it is the custom of poor people to have only a piece of bread. This was intended to give the person who recites the Haggadah the feeling of poverty and affliction.
And then, later in the Haggadah, we make reference to the fact that G‑d took us out of Egypt with great wealth.
Eliciting the Dynamic of Freedom
The point of the Seder is not just to relate events of the past but to elicit the spiritual dynamic of freedom and Redemption. Thus by mentioning and expressing our oppression and impoverishment together with our freedom and affluence, we empower ourselves to cope with these two challenges that stand in the way of our ability to serve G‑d uncompromisingly.
Moreover, by incorporating both poverty and wealth in our Seder we acquire the power to get out of exile, which has been characterized by the prophet as a state of both oppression and affluence:
“And those who are lost in the land of Ashur and cast away in the land of Egypt will prostrate themselves to G‑d at His holy mountain in Jerusalem.”
The reference to Ashur, is to the state of exile that is characterized by our immersion in materialistic pursuits—the test of wealth. Indeed, the word Ashur is cognate to the word for delight or wealth. The reference to Egypt is to those who are in a state of constriction, oppression and poverty.
Passover, at the Seder in particular, is the time to extricate ourselves from the shackles of exile, be they its oppressive and impoverished state, or its enticing and alluring attraction.
Decoding an Enigmatic Midrash
With this introduction we can decode an enigmatic statement in the Midrash:
“Rabbi Yosi ben Kisma was asked by his students: ‘When will the Son of David arrive?’ He replied, ‘This is the law of the Olah-burnt offering.’”
What is the connection between the Olah offering and the coming of Moshiach?
In light of the above discussion we see that the bringing of the burnt offering was a repudiation of the two forms of exile: its oppressive and impoverished state as well as its affluent form, which leads to assimilation.
When a Jew is prepared to sacrifice everything for G‑d notwithstanding the loss of income and the absence of a quid-pro-quo, is a sign that we have mastered the impediments of exile. When that occurs, Moshiach is ready to take us out of exile.
This can also be the deeper meaning of the words in the opening verse of the Parsha:
“It is the olah-offering that stays on the flame, on the Altar, all night until the morning…”
This reference to the offering remaining on the fire all night until the morning alludes to the sacrifices we make in the days of Galus that are likened to the night. When we meet the challenges of poverty and affluence all night it will lead us to the true and complete Redemption which is likened to the morning.