"And Hashem said to Moshe, saying; Command (tzav) Aharon and his sons, to say; this is the Law of the Olah...
The Parsha begins with Hashem instructing Moshe to command the Kohanim with regard to the Olah, a korban ('sacrifice' or 'offering'). Chazal note the use of the word, 'tzav' in the passuk; normally the Torah would say 'tell Aharon and his sons..' why here did the Torah use the stronger language of 'tzav'? The Medrash, quoted by Rashi explains that the word 'tzav' implies an extra sense of zerizus (alacrity) and that there was an extra necessity for this stronger language with regard to the Olah offering. Rebbe Shimon explains that there is an element of financial loss involved with this offering, therefore there was the concern that the Kohanim would be more hesitant in fulfilling the Mitzvo of Olah. Accordingly, it used the stronger language of 'tzav' in order to warn the Kohanim of the extra need for zerizus in bringing the Olah.
Rav Yechezkel Levenstein zt"l points out a remarkable lesson from this maamer Chazal (saying of the Rabbis). The Kohen Gadol was, in most instances, the most righteous and holy man of the generation. Moreover, the Gemara tells us that one of the prerequisites for being the Kohen Gadol is that he must be very wealthy. Based on the Kohen Gadol's great righteousness and wealth, it would have seemed unnecessary for the Torah to be concerned about a possible lack of alacrity as a result of a relatively small financial loss! Rav Levenstein explains that the Torah is teaching us that even the Kohen Gadol is subject to the yetser hara of love for money !
Chazal emphasize the power of the desire for money in a number of other places. One striking example of this is the Gemara in Bava Basra that discusses the most commonly transgressed aveiros. "Rav Yehuda said in the name of Rav, the majority of people [stumble] in theft, a minority [stumble] in immorality..." Rashi explains that the Gemara does not mean that the majority of people engage in blatant theft, rather they rationalize during their business dealings to withhold the money that others deserve. This Gemara teaches us how everyone is at risk of being enticed by the yetser hara for money to justify dishonest behavior that constitutes theft according to Torah law.
The greatest tzaddikim felt the power of the yetser hara for acquisition of money. Rav Yisroel Salanter zt"l once visited the home of a very wealthy man. The man had to step out of the room for a few minutes, leaving Rav Yisroel alone. When the man returned, Rav Yisroel was no longer in the room. He finally found Rav Yisroel standing outside the house. Rav Yisroel explained that there was a large amount of uncounted money in that room and Rav Yisroel did not want to be alone with that money. He explained by bringing the aforementioned Gemara that the majority of people stumble in theft and only a minority stumble in immorality. There is a prohibition of yichud to be alone with a woman because of the concern that one may not be able to overcome his temptation for immorality. Rav Yisroel concluded that if there is an issur yichud for fear of arayos of which only a minority stumble, then all the more so there should be an issur yichud with money, an area in which a majority stumble! Accordingly, he did not want to remain in the room alone with the uncounted money.
If someone such as Rav Yisroel Salanter felt a need for extra boundaries to protect himself from the temptations of money, then surely everyone needs to be extra vigilant of this powerful yetser hara. There are a number of areas in which such vigilance is necessary. Firstly, the lesson of this Parsha is that one must be careful that fear of loss of money does not harmfully effect one's fulfillment of Mitzvos. There are numerous Mitzvos that involve significant expenses, and one should strive to maintain the same alacrity in performing such Mitzvos as in less expensive Mitzvos. Moreover, one should be aware to maintain consistency in his spending on Mitzvos in comparison to his expenses on material comforts. If one elaborately spends on his vacations, home and car, then he should show a similar desire to spend money on Mitzvos in general and giving charity in particular. The Chofetz Chaim zt"l once encouraged a wealthy man to give more charity - the man felt that he was already giving a significant amount. The Chofetz Chaim showed him that he actually spent more on his drapery alone than what he gave in charity!
Another way in which love of money can hinder one's Avodas Hashem is that in areas of potential monetary loss a person may be tempted to 'bend' the laws of the Torah. Thus, an otherwise G-d fearing person, may be inclined to avoid asking shilos (halachic questions) to Rabbanim in areas of mammonos (monetary issues). Rav Yisroel Reisman Shlita once devoted a whole shiur to emphasizing that just as one would ask a shilo in areas related to kashrus and Shabbos, he should be careful to do the same in areas that are discussed in Choshen Mishpat.
It seems that the root of the desire for money is related to the 'slavery' that we try to uproot on Pesach. The sefarim discuss how freedom is not limited to being allowed to do as one pleases. The Torah conception of freedom means that one is not overly attached to the physical world. Love of money is one of the main ways in which a person can be subject to this form of 'slavery' - his desire for money hinders his ability to perform Mitzvos because he finds it difficult to part from it even when the Torah requires that he do so. On Pesach we emphasize our freedom from the physical world. This is symbolized by the Mitzvo to eat Matzo on Seder night, which is low and has no additions. So too, on Pesach we return to our pure essence, free of 'additions' such as material possessions which prevent us from serving Hashem properly. May Hashem grant us all a Pesach of true freedom from the yetser hara.
 Tzav, 6:1-2.
 There are different opinions as to the exact nature of the financial loss; many commentaries explain that unlike other korbanos, the Olah was fully burnt and the Kohanim were not allowed to eat from any part of it. Thus, he had a sense of loss in that in the time he was offering the Olah he could have offered a different korban from which he could have gained material benefit. See Ohr HaChaim, Tzav, 6:2 for an outline of other interpretations of the loss that Chazal refer to.
 Toras Kohanim, 6:1, quoted by Rashi, Tzav, 6:2.
 An exception to this is the Kohanim of the Second Temple period who often attained the position through bribery and political affiliations.
 Yoma, 18a.
 Tallelei Oros, Parshas Tzav, p.100, quoted by Meilitz Yosher.
 See Chagiga, 11b and Bava Basra, 165a. See also Mesillas Yesharim, Ch.11 who discusses these Gemaras.
 Translated as arayos. This refers to specific forms of immorality that the Torah prohibits in the strongest fashion such as relations with a married woman or incest.
 Bava Basra, 165a.
 Rav Yerucham Levovits zt"l brings Rav Yisroel's hanhago of never being alone with uncounted money. Rav Yerucham himself adds that he would even not want to be alone with counted money despite the heightened chance of being caught for stealing it! (Daas Chachmo u'Mussar, 4th Chelek, Parshas Shelach, p.115b.)
 Choshen Mishpat is the section of Shulchan Aruch that discusses monetary laws.