וַיַּ֣עַשׂ מֹשֶׁ֔ה כַּֽאֲשֶׁ֛ר צִוָּ֥ה יְהוָ֖ה אֹת֑וֹ וַתִּקָּהֵל֙ הָֽעֵדָ֔ה אֶל־פֶּ֖תַח אֹ֥הֶל מוֹעֵֽד׃
I uczynił Mojżesz, jako mu rozkazał Wiekuisty; i zgromadził się cały zbór u wejścia do przybytku zboru.
Or HaChaim
והקהל העדה, the community was assembled, etc. Perhaps when the people saw Moses taking Aaron, his sons, and the priestly garments, they assembled spontaneously. It is also possible that the verse tells us that G'd ordered the people to assemble around the entrance to the Tabernacle as explained by Vayikra Rabbah 10,9 on the word הקהל in verse 3 and that our verse reports that the people did so.
Rabbeinu Bahya
ותקהל העדה אל פתח אהל מועד, “and the assembly was gathered in the entrance of the Tent of Meeting.” This required a miracle, of course This is one of several places in the Bible where a very small area was able to accommodate a very large number of people (compare Tanchuma Tzav 12.). When Moses was told to assemble all the people at the entrance of the Tabernacle, he turned to G’d saying: “how can six hundred thousand men and six hundred thousand youngsters fit into the entrance [an area of 50 by 100 cubits] of the Tabernacle? G’d replied: “is this what you are concerned about? Was not the heaven at one time no bigger than the eye of a needle and I managed to fit the entire earth through it?” G’d quoted Isaiah 40,22: “Who spread out the skies like gauze, stretched them out like a tent to dwell in?” At the revelation at Mount Sinai G’d appeared surrounded by 22,000 chariots filled with ministering angels as we know from Psalms 68,18: ‘G’d’s chariots, myriads upon myriads, thousands upon thousands, the Lord is among them as in Sinai in holiness.’ Each of these chariots was similar to the one Ezekiel saw in his vision. Seeing this was so, how could the mountain have supported all these chariots? Clearly, miracles happened which temporarily suspended the rules applying to terrestrial space. At the time G’d had told the mountain: “expand and accommodate all the loyal people.” When the Jewish people crossed the Jordan river 40 years later the entire Jewish people found space between the staves of the Holy Ark behind the Priests who marched ahead. This is based on Joshua 3,9: “Joshua said to the Children of Israel: ‘come close and listen to the words of the Lord. your G’d.’” In the future these miracles will be re-enacted when all the people ever since Adam who qualify for resurrection will have to be accommodated on earth. Aren’t they going to complain that they do not find room to stand? However, G’d promised that at that time “I will expand the size of Jerusalem” as prophesied by Isaiah 54,2 who quotes G’d as addressing Jerusalem saying to her: “enlarge the size of your tent, extend the size of your dwelling; do not stint!” Thus far the comments of the Midrash Tanchuma Tzav 12 on the subject.
Tze'enah Ure'enah
“When the community was assembled at the entrance of the Tent of Meeting” [8:4]. It was a great miracle that all of Israel stood before the door of the Tabernacle. There were six hundred thousand Israelites. How were they able to stand before a door that was not so big? Moses wondered about this and said at first, how is this possible to have all of Israel stand there? They are six hundred thousand men and their youths are also six hundred thousand. The Holy One responded: what kind of wonder is this for Me? I stretched the heavens very far from one thin thread. Similarly at Mount Sinai, how many millions of angels and how many thousands of Israelites were there? How could they all stand at Mount Sinai, but the Holy One said to the mountain, stretch and make yourself wide. So too at the door of the Tabernacle, the Holy One also said, expand and receive all of Israel. Similarly, when the Messiah will come, all the dead, from Adam until the coming of the Messiah, will be resurrected. These dead and also may other people will all be in Jerusalem. Should the Holy One not expand the city of Jerusalem, it would not be possible to receive all the people.10Bahya, Leviticus, 8:4.