Around this time of the year, specifically on the 23rd of Adar, which is April 2nd this year, Moshe started practicing erecting the Mishkan according to the Ramban in this week’s Torah portion of Tzav.
The Ramban says, “Rather, the correct interpretation is that we say that Moshe was commanded about the assembly of the Tabernacle (Mishkan) on the twenty-third day of Adar, and he assembled it [on that day]. As soon as the Tabernacle stood in its position, G-D, blessed be He, Who sits upon the Keruvim, called Moshe and commanded him about the actions involved in the bringing of the offerings — all those sections from the beginning of the Book of Vayikra until here. [This was because] He wanted to teach him the actions and statutes of all the offerings before he offered up any of them, since among the initiation-offerings were the sin-offering, burnt-offering and peace-offering, and they could only know all their laws from these sections with which He preceded [to command him]. Afterwards He said to him, Take Aharon and his sons with him etc., to urge him on when the time came for performing what He had told him at first — And this is the thing that you shall do unto them to hallow them, to minister unto Me etc., adding here, And you shall assemble all the congregation at the door of the Tent of Meeting, so that it should be done in the presence of all of them, that they should know that G-D, blessed be He, chose Aharon and his sons [to minister unto Him].
By way of the proper interpretation of Scripture, Moshe was commanded about the building of the Tabernacle prior to the incident of the golden calf [as is the order of these chapters in the Book of Shemos], and when the Holy One, blessed be He, became reconciled to him and promised him that He would cause His Divine Glory to dwell among them, Moshe understood of his own accord that the command concerning the Mishkan remained valid as before, and he then commanded Israel regarding it, as I have explained in the section of Vayakheil. After they had completed the work, he was then told the section of, On the first day of the first month shall you set up the Tabernacle of the Tent of Meeting, and he was then told, And you shall bring Aharon and his sons unto the door of the Tent of Meeting etc. Thus Moshe knew that Aharon and his sons also remained in their esteemed and beloved position before G-d. Here, He urged them again on the first day of the consecration, at the time of performing the command [And you shall bring Aharon and his sons etc.] Thus all the sections of the Torah are in chronological order, except that He placed before its sequence the verse, And the cloud covered the Tent of Meeting (Shemos 40:34), which in the opinion of our Rabbis was on the eighth day of the initiation, in order to arrange in order the whole matter of the assembly of the Mishkan, it being the customary way of Scripture in all places to finish a subject that it has started to explain.” (Click here for Hebrew text.)
The Ramban is of the opinion that the Torah for the most part is written in chronological order therefore, Hashem first told Moshe about building the Mishkan (in Ki Sisa) before the sin of the golden calf. Then, after Hashem was appeased by Moshe’s prayers on behalf of the Jewish people and promised to rest his Shechina amongst them, meaning that He wanted the Mishkan built, then the Jews started building the Mishkan (in Vayakhel 35:1). After they finished building it, Hashem told them to put it together and they will start using the Mishkan on the first of Nissan at its consecration (this is mentioned in Pekudei 40:2, 12). Hashem then taught many of the laws about the various types of sacrifices that will be used in the inauguration of the Mishkan, (this is mentioned in Vayikra and the beginning of Tzav.) Finally, at this point (perek 8 in Tzav) on the 23rd of Adar, Moshe anoints Aharon and his family and practices, for the next 8 days, putting together and taking apart the Mishkan, as well as performing parts of the service until the ultimate inauguration of the Mishkan in the beginning of the Torah portion of Shemini, that will be read next week.
Among all this, the Ramban mentions after Hashem told Moshe to teach everyone about the laws of the sacrifices that Moshe should, “Take Aharon along with his sons, and the vestments, the anointing oil, the bull of sin offering, the two rams, and the basket of unleavened bread (Vayikra 8:2). Hashem told Moshe this, according to the Ramban, in order “to urge him on when the time came for performing what He had told him at first.” Meaning, Hashem told Moshe to ensure that Aharon and his sons acted with zrizus, alacrity, when performing G-D’s service. Why did Hashem, at this juncture, have to urge the kohanim to act with alacrity (zrizus) when performing G-D’s service? They were proven to be committed to serving Hashem, as the Ramban himself mentioned right before this request to urge them to perform with alacrity as he said, “Thus Moshe knew that Aharon and his sons also remained in their esteemed and beloved position before G-d.” Also, how can they let anyone down at such an ostentatious time, isn’t it obvious that they should get to work with the utmost speed and alacrity, why do they have to be reminded? If so, what does the Ramban mean when he says, “He urged them again on the first day of the consecration, at the time of performing the command?”
However, if you look at the chronology of events where Hashem just taught a whole slew of laws of how to work in the Mishkan, i.e, the sacrificial service, then it’s the proper thing to refocus and urge them to perform with alacrity. This is because it is human nature for people to become overwhelmed when thrown at them a whole bunch of rules, no matter how great they are, so by reenforcing the resolve to perform with zerizus (alacrity) it refocused them to start off on the right foot.
This is an incredible lesson in communication that, when giving a whole list of instructions, review the general purpose of the instructions at the very end so that the person being instructed can regain his or her baring and quickly get onto fulfilling what they were instructed to do.