Parshas Vayikra addresses itself primarily to Mikdash service (Avodah) of the individual. Whereas Parshas Tzav is concerned with the daily Mikdash routine as performed by the Kohanim, which is of a more public nature, Parshas Vayikra deals with voluntary korbonos (v. Rashi on 1:2) as well as with instances when individuals and specific groups would need to offer for particular purposes.

Surely, the sacrificial regimen of Parshas Tzav was more common than much of the Avodah featured in Parshas Vayikra; why, then, does Parshas Vayikra precede Parshas Tzav?

It is noteworthy that Rashi, at the beginning of our parshah (1:1), quotes several statements from Chazal which explain that Hashem communicated with Moshe in a loving manner, that Moshe was specially privileged to be in close contact with Hashem such that no one else could hear Hashem's voice when it reached Moshe, and that Hashem's communication with Moshe reflected the favor of B'nei Yisroel in Hashem's eyes. Divine speech with Moshe had obviously commenced much earlier, so why does Rashi elaborate upon its nature at this juncture? Why does the Torah use the term "Vayikra", indicative of Hashem's adoration, at this point?

It would seem that we are being taught a lesson about how to relate to and serve Hashem. Formal Avodah, which is first presented in Parshas Vayikra, must be based on each individual's commitment to Hashem. This commitment is a prerequisite for any formal Avodah. And the same is true regarding communal service, such as that of the Kohanim on behalf of the larger public: it can be meaningful only after each individual has already set forth a desire to cleave to Hashem and maintain a connection with Him. This is why Parshas Vayikra, whose focus is private Avodah, must precede Parshas Tzav, which features public Avodah. And for the same reason must the Chazaras Ha-Shatz, in which the chazzan recites Shmoneh Esrei on behalf of the tzibbur as a whole, be preceded by the private Shmoneh Esrei, as an individual connection to Hashem must be established in order for one to be meaningfully represented in public service.

We can now understand why Hashem's private communication with Moshe is especially highlighted so as to serve as the preface for Parshas Vayikra, and why it is emphasized that Hashem's communication with Moshe was indicative of a special love, for we are being taught that a private attachment to Hashem is a prerequisite for formal Avodah. And just as korbonos without inner feelings of repentance, love and supplication on behalf of the donors are meaningless, public Avodah without the prior commitment of each member of the tzibbur is sorely deficient.

May we strengthen our private, individual commitment to Hashem, as well as our communal service of Him, and may the entire K'nesses Yisroel soon merit the return of Avodah in its fullest sense.