Why does it say "Hoy"?
Rashi: It is an expression of calling out, designation and gathering. It occurs often, e.g. "Hoy Hoy v'Nusu me'Eretz Tzafon" (Zecharyah 2:10).
Does this literally discuss one who is thirsty?
Rashi, from Bava Kama 17a:"Water" refers to Torah.
Radak: Water is a metaphor for Torah and Chachmah. Just like the world cannot exist without water, it cannot exist without Chachmah. Just like one who is thirsty desires water, so the intellectual Nefesh desires Torah and Chachmah - "Lo Ra'av la'Lechem v'Lo Tzamei la'Mayim Ki Im Lishmo'a Es Divrei Hashem" (Amos 8:11).
What do we learn from "Kol Tzamei Lechu la'Mayim"?
Kidushin 30b: If this disgusting one (the Yetzer Ra) encounters you, drag it to the Beis Medrash.
Radak: After war of Gog and Magog, the Nochrim will recognize that Hashem rules over all, and there is none other than Him. They will come to Yerushalayim to learn His Mishpatim and Torah - "Lechu v'Na'aleh El Har Hashem... va'Yorenu mi'Derachav" (2:3). It is as if the verse calls them to come to learn.
Malbim: The Nevi'im compare Torah and Mitzvos to bread and water 3
, for they are the food of the Nefesh, just like bread and water are food of the body - "Lo Al ha'Lechem Levado Yichyeh ha'Adam" (Devarim 8:3). Just like in bodily food, there are things that a person cannot live for a moment without them, e.g. water, and it is found cheap or for free, and there are foods such as bread that one buys for money, so in mindsets and deeds, there are some of them that the Nefesh cannot live properly without them, e.g. Emunah in Hashem's existence and Hashgachah. There are deeds that even codes of etiquette mandate, e.g. [not] murdering and stealing. These are like water. Also refer to 55:1:7:2.
Here it says that the thirsty should go to water. Above (21:14), it says to give water to the thirsty!
Ta'anis 7a: If he is a proper Chacham, give water (teach) to him. If not, he himself will go [to learn].
What is the meaning of "Shivru"?
Rashi: This is like "Lishbor Bar" (Bereishis 42:3), i.e. to buy.
Why does it say "b'Lo Chesef uv'Lo Mechir"?
Radak: They will give to you for free.
Malbim: This refers to the Navi's words in Perek 50. He addressed his generation, who believed in the false Nevi'im's words, which they prophesized for money. Here he says, come to Mayim, i.e. learn matters that the Nefesh needs like water, and even one who does not have money. Also buy and 'eat' things like bread - you will find them without money. Also wine and milk, which are just for pleasure, are for free.
Ma'alos ha'Torah (DH Yafutzu): Torah is compared to water - it is always free. Do not say that just like water has no price, also Divrei Torah - "Yekarah Hi mi'Peninim" (Mishlei 3:15).
Does this literally refer to wine and milk?
Rashi: No - it is a purchase better than wine and milk (i.e. Torah). Radak - Torah is metaphorically called wine - just like wine gladdens the heart, "v'Yayin Yismach Levav Enosh" (Tehilim 104:15), also Divrei Torah - "Pekudei Hashem Yesharim Mesamchei Lev" (ibid. 19:9). And just like milk sustains a nursing baby and makes him grow, so Divrei Torah sustain the Neshamah and make it ascend in level.
Malbim: No. There are matters that are like bread - learning Torah and its Mitzvos, and constant Mitzvos such as Tefilah and Shabbos. Just like there are matters that the body can live without them, and they were created only for pleasure, the same applies to food of the Nefesh, e.g. knowing ideas and knowing every matter to its truth. There are Mitzvos that are Midas Chasidus; these are like wine and milk, which are only for pleasure.
