At the beginning of the Parsha, the word "Tzav," is used to command Aharon and his sons concerning the Korbanos (ויקרא ו':ב'). The Malbim explains that the word "Tzav" has three meanings, referring to urgency, immediacy, and relevance for future generations. Rashi (שם בד"ה צו) quotes Rabbi Shimon who says that the word "Tzav" is used where there is a monetary loss involved; the Torah is thus mindful to call attention to the need for urgency. This means that when the Torah uses the word "Tzav," it means to tell us that in this case, where there is a monetary loss, the Torah cares more about the need for urgency.
It is somewhat unclear, however, as to whether Rabbi Shimon is disagreeing with the other definitions of the word "Tzav" mentioned above, or merely adding to them. The Ramban says that perhaps Rabbi Shimon was arguing with the other interpretations of the word "Tzav," saying that according to the other interpretations, the word "Tzav" is used to identify a Mitzvah which is in effect immediately and for the future, while he believes it is used because of the urgency needed in a case where there is a monetary loss. Rabbi Shimon is thus coming to argue with the previous definitions. However, this explanation is generally not accepted, and the Ramban himself says that Rabbi Shimon is not rejecting the other definitions because he is not talking about the same topic. The word "Tzav" here is used specifically to refer to the Korban Olah; Rabbi Shimon's explanation, referring to a monetary loss, is not related to this, because the Kohanim suffer no monetary loss from it. On the contrary, the Ramban says, they gain from it because even though the animal itself is completely burnt, the Kohanim keep the hide of the animal. Thus in this case, Rabbi Shimon can accept the other definitions.
The Kesav Sofer also says that Rabbi Shimon is merely adding on to the other interpretations, but that he is talking specifically about certain other Korbanos paid for by the Kohanim out of their own resources. However, this explanation is difficult, for if Rabbi Shimon is indeed adding on to the other interpretations, then why does he stress a need here for urgency (which is one of the Malbim's interpretations of the word) in the bringing of these Korbanos? After all, there is no financial loss since the Kohanim could just take the items needed for these Korbanos out of the Terumah that they are given. The answer is that at the time this Mitzvah was given, the Jews were still in the desert and the Kohanim were thus not yet getting Terumah. For the Kohanim to get the items needed for these Korbanos, they had to either buy them or hire merchants to travel a far distance for them. Therefore, urgency was needed because there was a monetary loss. It is thus possible that all the different meanings of the word "Tzav" are relevant to our Parsha.