What does "Ach" come to preclude?
Rashi: It comes to preclude Yehoshua and Calev, who were given their portion in Eretz Yisrael without lots. 1
Seforno: Even though the portions were divided up according to size, 2 the division was made exclusively by means of lots.
How was the Goral actually carried out?
Rashi (on Pasuk 54, citing Bava Basra, 122a): Elazar the Kohen Gadol, who was wearing the Urim v'Tumim, announced with Ru'ach ha'Kodesh "In the event that Shevet Ploni emerges, the following borders will emerge together with it!" The names of the tribes were written on 12 1 slips, and the 12 areas of Eretz Yisrael on 12 slips. He mixed the slips in a box and the Nasi of the named tribe would place his hand inside the box and draw two slips
'Twelve' implies that also Gad and Reuven were in the lottery, i.e. Hashem will cause them to pick portions in Ever ha'Yarden to show that Hashem agree d that they inherit there. However, Bamidbar 34:19-28 names the Nesi'im for the lottery, and omits Gad and Reuven! The Ibn Ezra and R. Bechayei say that they were not in the lottery, since they already received their portions; I did not find anyone who disagrees. It seems that Rashi wrote '12' to denote all the Shevatim, but it is not precise. (PF)
Rashi: 'Finally, based on the Pasuk later (Pasuk 56), "Al-pi ha'Goral", the lot would announce "I, the lot of G'vul P'loni, emerged for Sheivet P'loni!" '
What are the connotations of "li'Shmos Matos Avosam Yinchalu"?
Rashi #1: Having insinuated earlier 1 that the land was to be distributed according to those who were about to enter Eretz Yisrael and who were being counted now, the Torah is now teaching us that, unlike all other cases of inheritance in the Torah, the inheritance here first went back to those who left Egypt 2 who had already died, and the living now inherited the deceased (from the grave). 3
Rashi #2: It automatically precludes Geirim and Avadim from receiving a portion.
In Pasuk 53. See Sifsei Chachamim.
Rashi learns this from the word "Matos", Ramban and Moshav Zekenim learn this from the word "Avosam," since 'Matos' is synonymous with 'Shevet', meaning 'tribe', as we find frequently (See Ramban).
Rashi: Consequently, if two brothers (neither a firstborn) left Egypt, one leaving one son who entered Eretz Yisrael, the other one three sons, the former received one portion, and the latter, three. The four portions then went back to their grandfather, who bequeathed them equally
How could they rely on the Goral? Yehudah had the most people; it needed to receive the biggest portion. If one of the portions was larger, perhaps it will fall to another Shevet!
Kol Eliyahu: Initially they made equal portions. After casting the lot, they took from the smaller Shevatim and gave to the bigger
Rashi writes that the portions go back to their grandfather, who bequeaths them
Moshav Zekenim: Indeed, if their father was above 20 when he left Egypt, this suffices. Rashi discusses when the father was less than 20, so then it must go back further, to one who was 20 when he left.