The Holy Alshich writes the following on this verse -
In this verse it's not written 'in it' (implying HaShem will dwell in the sanctuary), rather it says 'in them', implying that the divine presence can rest inside each and every Israelite.
As so, we can see from the below verse from King David that the human acts as a sanctified vessel for the Divine presence to rest upon.
Based on this understanding we can ask why there was a need for HaShems commandment to build a centralized Tabernacle for the Divine presence to rest, if in fact that presence was made to rest inside of all of man and dwells inside of all the people of Israel?
We will now look into the Tanna Debei Eliyahu for some clarity -
So our first question is why the children of Israel accepting the laws of HaShem immediately leads into the commandment to make a Tabernacle.. what do the two have to do with each other that the Torah flows from one scenario right into the next.
Let us say with the help of Heaven that a principal concept in receiving and up-keeping the Torah is only through the collective unity that exists amongst the People of Israel, in which everyone loves their friend as they would themselves.
As the verse in the Torah states -
This is teaching that prior to the receiving of the Torah, the condition for the Israelites was that they must stand in total unity with each other, and only through that will they be able to receive the Torah, and similarly, this unity is what causes the upkeep of the Torah, because through unity, it is as if all of the people of Israel are collectively keeping the entirety of the Torah!
This is similar to what was said in the writings of Beit Shmuel Acharon to explain the below famous story from the Talmud -
Based on this fascinating story, the Maharsha explains that this is the commandment of 'Love your brother as you love thyself' (shown below), and through this one can actually keep the entirety of the Torah.
So the Beit Shmuel comes to explain how this one commandment is as if you are keeping the entire Torah. Behold, it is written in the many books of wisdom from the sages, that every Israelite MUST keep the entire 613 Commandments, and if you don't keep all of the Commandments, you must come back down to Earth as a reincarnation an additional time to keep these Commandments. Yet we can see that many of the Commandments are set up in a way in which its not possible for everyone to keep them all, for example the Mitzvah of Levirate Marriage, and the Mitzvah to circumcise if you don't have a son. So for whoever doesn't have a brother that passed away childless (Levirate Marriage), how can we save this person from having to come back in a reincarnation?!
The answer is that if he kept the Mitzvah of Love your neighbor as you love thyself, which in that case the people of Israel are considered one person, one body, and you get included in the Mitzvot (Commandments) of your brethren who keep the ones you cannot!
And the deeper meaning of the story above re: the convert is that this potential convert was afraid that he would convert and then have to be reincarnated. Regel, leg, as the convert wanted to stand on one leg, can also mean time, occurrence, or trip - as we can see it being used in the below verse -
So the convert was saying, convert me on the condition that I can keep and learn the whole Torah while standing on one leg, which means to say that I want to convert, but how can I do this all in one lifetime without needing to come back as a reincarnation? On this question Hillel gave an exact answer and said to him to just love your neighbor as you love thyself, and this way you are fulfilling that commandment from the Torah, and this allows you to keep the whole Torah in one shot, even if you personally don't do all the commandments, you fulfill what the people of Israel collectively fulfills!
And on this the Sages of Israel comment on the below Talmud -
This is such a great principal since from the love we have for our people, Israel, we all have a share in the complete fulfillment of the Torah, hence, a great principal!
And now we can fully understand why HaShem commanded the Israelites to build a Tabernacle. That the Tabernacle is a unifying force for the people of Israel, since they have to come three times a year, and when the time for the King to recite the Torah, as well there is a gathering of men, women and children around it, and through this it is as if all of the people of Israel are considered one, and our Mitzvot get pooled together. This is why the verse says 'Build for me a sanctuary' and through this the people of Israel will act as one, and a direct result of this unity it will be as if all the people of Israel are keeping the entire Torah, and then this causes the end of the verse to happen - 'so that I may dwell within them', which is the divine presence resting amongst us all, because as a result of keeping the Torah, the Divine rests upon the keeper.
And this knowledge can explain the above teaching from the Tanna D'Bei Eliyahu - that when the people of Israel said 'we will do and we shall listen', HaShem replies back right away, OK sure, in that case, build for Me a Tabernacle. Because how is it possible for each Israelite to upkeep the entire Torah as we discussed before? However, through the Tabernacle for HaShem, a unity amongst Israel is formed, and through this unity it is as if we are keeping the entire Torah! And then from this we are worthy that HaShem's presence dwells inside of us individually.
And behold, now in the time of exile, where we don't have a Temple or Tabernacle to come and visit, the advice to add unity amongst the people of Israel is to gather in the houses of prayer and the houses of study, as they are 'mini sanctuaries', and to gather for Torah learning and prayer with a congregation, and through this, even today we can be considered on the level of up-keeping the entire Torah.
And this explains the below teaching from the sages -
And Rashi clarifies this -
And the intention here based on our thought process, that the functionality of the houses of study and houses of prayer, is the medium for the oneness between our people as we spoke about earlier. And with this Bilaam wanted to curse the people of Israel, that they should have no houses of worship and houses of prayer, as he knew that the unity amongst the people of Israel was the secret of Israel keeping the Torah, and the causality of the Divine Presence resting amongst them.