Why does the Torah write "Ki Seitzei Eish", insinuating that the fire spreads by itself?
Rashi: Because if one allows a fire to spread without keeping it under control, one is liable for damages, 1 (since he should have taken into account the regular wind which carries the flames from one location to the other
In fact, the Torah considers it as if he set fire to the damaged segment of the field - as the Pasuk concludes (Rashi, Targum Onkelos and Targum Yonasan).
What are the connotations of "O ha'Sadeh"?
Rashi and Rashbam: If the fire destroys the furrows in one's neighbor's field, requiring the owner to plow it a second time, one is liable to pay.
Why does the Torah see fit to mention both thorns, and a haystack?
Bava Kama, 60a: Had the Torah mentioned only thorns or only haystacks, we would have thought that the former are subject to Eish because they stand to be burnt and people tend to be negligent concerning them; and the latter, because it is valuable. Therefore the Torah saw fit to mention both.
Oznayim la'Torah: The Torah is listing 'Lo Zu, AF Zu (from the most obvious to the least obvious): 1. Thorns (Refer to 22:5:3:2); 2. a haystack which is generally dry and prone to catch fire; 3. standing corn, which is still moist and less prone to catch fire; 4. furrows and stones, which are the least likely to burn.
Why does the Torah see fit to add standing corn and the field?
Bava Kama, 60a #1: The Torah mentions "Kamah" to teach us that Eish is only Chayav fo what is revealed, but not what is hidden, 1 and Sadeh to include a fire that burnt the furrows or scorched the stones in the field
For example, money or anything else that one does not normally place inside a haystack
Why does the Torah write "ha'Mav'ir es ha'Be'erah", since it is obvious that it is he who pays?
Bava Kama 60b: This refers to Hakadosh-Baruch-Hu, who says - 'I lit the fire in Tziyon, which destroyed its foundations (Eichah 4:11), and I will rebuild it with fire,' 1 as the Pasuk writes in Zecharyah 2:9 "And I will be for it a wall of fire all round, and for glory I will be in its midst".
Bava Kama: To teach us that there si no fixed Shi'ur for Eish as to how far the fire must travel in order to be Chayav, but that it depends on the velocity of the fire. 2
Chidushei Agados (Maharal, 60b) - since Chisaron came through the epitome of perfection, it is proper that He complete the Chisaron. He struck (to cleanse Yisrael from sin), and He heals it. Maharsha (60b) - He heals with the same matter that he used to hit, unlike people.
Oznayim la'Torah: Because a powerful fire can travel even a thousand Mil.