VaYakheil and Pekudei are usually seen as parallel Parshiyot. VaYakheil is a review of the construction of the Mishkan and Pekudei is a review of the Bigdei Kehunah. There is, however, an inconsistency in the Parshiyot: in Pekudei, the phrase “KaAsher Tzivah Hashem Et Moshe,” “As Hashem commanded Moshe,” frequents the Parashah, appearing in almost every section. VaYakheil, however, does not once use this phrase. The Brisker Rav explains this inconsistency. The Gemara (Kiddushin 29a) teaches that whenever the verb “Tzivah” or “command” is used, it teaches that the command was not only for that time, but for the future as well. This explains the inconsistency. The Mishkan was a one-time Mitzvah built specifically for the desert; when we came to Israel, we would build a Beit HaMikdash, and we would no longer need to know how to build the Mishkan. The Bigdei Kehunah, however, would be used again in the Beit HaMikdash, and we would therefore need to know the laws for the future; therefore, the verb “Tzav” is applicable.
An objection is raised to this answer: while VaYakheil does deal with the construction of the Mishkan, it also deals with some of the Keilim that were in the Mishkan, such as the Menorah and the Shulchan; why isn’t the verb “command” used in those cases? The answer to this, the Brisker Rav explains, is that while these figures, such as the weight of the Menorah and the number of knobs on it, are applicable for all times, the exact form and shape had to follow specific instruction given by Moshe through Nevuah, and this small facet, used only in the desert, would not be used for future generations. Such an aspect did not apply to the Bigdei Kehunah (the Bigdei Kehunah never changed from the description in the Torah), so the word “command” is still applicable.
This idea can be used to explain a difficult Tosefta in the seventh Perek of Menachot. The Tosefta quotes Pasuk 23 of Perek 40, which states that Moshe placed the bread as Hashem commanded, and Pasuk 25, which says he lit the candles of the Menorah as Hashem commanded. The Tosefta asks where we see that Hashem commanded Moshe to do these things, and then answers that the command came from VaYikra Perek 24.
This answer seems very strange as the Tosefta needed only to state that the source for the command came a few Pesukim earlier in Shemot 40:4 where Hashem tells Moshe that he should set up the bread and light the candles. Why did the Tosefta need to look in Sefer VaYikra for the source? The Brisker Rav uses the aforementioned idea to answer the question. He explains that when Hashem told Moshe to set up the bread and light the candles in Pasuk 4, this was done as part of the inaugural ceremony for the Mishkan, not as a ritual to be done for the generations. Therefore, this verse could not be applied to Hashem’s command for the weekly ritual of placing the breads and the daily ritual of lighting the candles, both of which would take place for generations to come. As such, the Tosefta needed to locate another source upon which the actual ritual was based, a source found only in Sefer VaYikra.