The Mishna in Pirkei Avos (ch 5) tells us that one of the miracles that took place at the time of the Mikdash was that no one ever complained of being cramped for space in Yerushalayim. Chasam Sofer and others explain that the miracle the Mishna refers to has nothing to do with the physical space of Yerushalayim – the city boundaries did not magically grow bigger when crowds came. Rather, what happened is that people’s attitude changed. The same people that may have complained that their little home is too small, their kitchen is too cramped (what Jewish housewife does not long for a bigger kitchen?), having to sleep in bunk beds and share rooms is not fair, etc. forgot all that once they came to Yerushalayim. Even if the physical conditions might have been worse than at home, when you have the opportunity to come to Yerushalayim and be in the presence of the Shechina, who thinks of how big the hotel suite is? Does it really matter if your neighbor bumps into you a little if you have the opportunity to see avodah taking place? Three times a year thousands of people came to Yerushalayim for aliya la’regel and somehow, three times a year they all made space for each other and got along because they felt Hashem’s presence and therefore nothing else mattered.
Now we can understand what the donkey was asking Bilam. The malach was not out to harm Bilam, but rather was a malach of rachamim sent to stop him from doing something silly. Chazal tell us that whenever the malach Michoel (=rachamim) is present, the Shechina is right there with him, close by. So true, Bilam’s foot had been banged into the wall three times – there was no room to move. But when the Shecha is present, who thinks about how much or how little room they have? Who feels cramped and complains? The donkey asked Bilam, “How can you even feel that bump when there is so much else you should be paying attention to now?”
And now we understand as well why it is davka the shalosh regalim that are alluded to in the donkey’s question. These three times a year when all of Klal Yisrael gathered in Yerushalayim and no one complained about lack of space, no one complained about being crushed by the crowds or someone bumping into him, proved the donkey’s point – when you have the Shecina on your mind and have an awareness of what being in Hashem’s presence means, nothing else should bother you. If it does, you are at fault. (Based on Midrash Moshe)
R’ Ovadya writes in a teshuvah (Yechaveh Da’at vol 1) that there is still a kiyum mitzvah of aliya la’regel in our times. The Ran in Ta’anis (bottom of 2a in pages of the RI”F) writes that even after the churban, Jews would still gather in Yerushalayim and come to the mikdash for the regalim. (Side point: the Ran is justifying why in Eretz Yisrael the day to start asking for rain in davening, which is fixed based on the assumption of how long it would take for someone to get home after making aliya la’regel, remains the same even after the churban. Why is this a question? Once the date was fixed, shouldn’t the takanah still stand even if the reason no longer applies, so long as there is no beis din gadol b’chochma u’minyan to repeal it?) Tashbeitz echoes the same, and adds that even in his times, this nes/bracha of no one complaining of lack of space still held true. The kedusha of Yerushalayim is eternal because it is the presence of the Shechina; that presence influences the character and attitude of those who visit and those who live there (and maybe even those who aspire to live there) to our very day.