The answer is that since their travels were by the commandment of Hashem so their place was wherever Hashem commanded them to go. So even though they dismantled the Mishkan in one place and then rebuilt elsewhere, they were only in one place, where Hashem commanded them to be.
So from this Chazal understood that the prohibition of demolishing on Shabbos is to rebuild in the same place.
(Like by every one of the 39 Melachos of Shabbos there is the Av Melacha the original prohibition and there are the similarities, some of which are included in the actual Melacha and some which are not include but are similar and our Rabbis added them as well.)
What does this mean to us?
If we want to be connected to Hashem and be redeemed from all worldly pressures the only way is to follow what Hashem wants from us every moment of our life. When we put aside our personal calculations and follow fully what Hashem wants even though it may look like it’s not to our benefit; but if we do what’s correct then we are redeemed from the clutches of this world and in the long term more successful.
In the town of Brisk there were elections for the board of the Jewish community. On one side was the Brisker Rav and those that were following his rulings. On the other side were a group of people looking to ease off on all religious laws. They wanted to remove the Rav's Kashrus certificate from the butcher, stop the funding for the Jewish education and much more. The campaign was run mainly by posting up signs in the streets and in the Shuls. Each side explained the importance of their view and what was wrong with the other party.
The elections were to take place on Motzaei Shabbos. The last signs were going to go up on Friday.
The Rav's followers went over the last sign and what had to be highlighted just before the elections. The paper was given in to the printer to be printed.
Shortly after a copy of their sign was given to the other party. There was a massive uproar. Every word of the Rabbis sign was so true and convincing. The other party decided to prepare a sign fiercely attacking the religious party very sharply. The sign personally attacked the Rav, the candidates and everything they stood for.
The printer had a difficult job getting ready two signs in time for Shabbos. In those days every letter had to be put on a massive plate until the whole page was ready. It wasn't a quick job.
The posters arrived late Friday afternoon. They brought one to the Rav to show him. He asked where were the rest of the posters? He asked to see them all. He took all of them and put them in his study.
His supporters were in shock.
The Rav explained that since it was late it was inevitable to hang up the posters before Shabbos and therefore it would involve desecration of the Shabbos.
They tried to explain to the Rav that for sure the opposing party had prepared very powerful posters and it was very important to voice their opinion.
The Rav didn’t budge.
And as everyone went to Shul they all stopped to read the posters being hung up as Shabbos had already come in. The posters were so sharp and so belittling the Rav; the local townspeople were in total shock. Why such behavior against the Rav? So much so that they were so angry most of them voted in favor of the Rav's candidates.
Had the other signs gone up on the walls everyone would have understood that one sign was answering back against the other. But now there was no valid reason for such behavior.
So in the end by listening to the Brisker Rav and being extra careful to keep Shabbos ended playing in their favor.
