Moshe erected the Mishkan on rosh chodesh Nisan, as it states (Vayikra 9:1), בַּיּוֹם וַיְהִיְּׁמ ִינִיהַש, "It was on the eighth day..." Rashi writes, "It was the eighth day of the Milu'im, rosh chodesh Nisan. It was on this day that the Mishkan was erected."
Also, in this week's parashah it states (40:17-18) הַמ ִּשְׁכָּן הוּקַם ׁל ַחֹדֶש בְּאֶחָד ...הָרִאש ׁוֹן ׁבַּחֹדֶש וַיְהִי, "It was in the first month (Nisan)... on the first day of the month that the Mishkan was erected."
Before the Mishkan was officially erected, there was a seven-day period called the שבעת המלואים ימי, to sanctify the kohanim and the mizbeiach for the upcoming avodah. Every day of the seven days of Miluim, Moshe would erect the Mishkan, perform the avodah, and then dismantle the Mishkan. This occurred every day, until the eighth day, which was rosh chodesh Nisan. On that day, Moshe erected the Mishkan, and it remained standing, by day and by night (until they traveled).
The Midrash (Tanchuma, Ki Sisa 35) states a machlokes, whether Moshe erected and dismantled the Mishkan twice each day of the seven days of Miluim, or three times each day.
The fact that the Torah tells us that the Mishkan was built on the eighth day, it implies that during the seven days of Miluim, even if it was built temporarily to perform the avodah of those days, it was immediately taken down.
What is the reason for this pattern? Why couldn't the Mishkan be built and left to stand? Why was it built and dismantled over and over again? The Ramban (40:2) deals with this question.
Nesivos Shalom zt'l explains that the Mishkan was built, taken down, built up again, and taken down, to give chizuk to the Yidden. Every Yid should turn himself into a Mishkan, a place where the Shechinah resides. When he serves Hashem well, he is a Mishkan. But there will be times when he will fail in his avodas Hashem, and he will sin, chalilah. When this occurs, it is like the Mishkan was taken down. But he should know that there will be good times again. He will soon perform good deeds, and the Shechinah will reside on him once again.
As we wrote, there is an opinion that the Mishkan was built and dismantled three times. This happened for seven days. According to one view, the Mishkan was built and dismantled 21 times during the seven days of miluim. (3 x 7 = 21.) These 21 times is the gematria ה"אהי. The translation of ה"אהי is "I will be." This means that when one falls, he should tell himself, "The next time will be different. The next time, I will be good. ה"אהי, I will be as Hashem wants me to be." It isn't easy to keep saying this, especially after falling 21 times, and he feels that he can never succeed. But if he continuously keeps trying, he will succeed in the end.
The Nesivos Shalom quotes from the Beis Avraham ה"אהי times ה"אהי (i21x 21) equals the gematria of ת"אמ. "This is because the אמת is that even if a Yid accepted upon himself many times to be good, and still he fell again, nevertheless, he should try again. If he does so, the truth is that Hashem will accept him with love."
Shabbos HaChodesh gives us the message of "Renew yourself. תתחדש. What was until now, was. Now start again. Don't remain in your fallen state. Pick yourself up and maybe this time you will succeed in being as a Yid should be.
Tzaddikim have said that this is the segulah of this Shabbos, to begin again, to begin anew.
The first mitzvah given to Bnei Yisrael is the mitzvah of kidush hachodesh (see Rashi, Bereishis 1:1). We can explain that it is the first mitzvah because the attitude of making oneself new and starting over again is the first step and the foundation of avodas Hashem. Just as the moon becomes new each month, we should work to forget about the past and make the future better.
