The Gemara answers: We derives it from that which Rabbi Yehoshua ben Korḥa says, as Rabbi Yehoshua ben Korḥa says: From where is it derived that the legal status of a person’s agent is like that of themself? As it is stated with regard to the Paschal offering: “And the whole assembly of the congregation of Israel shall slaughter it in the afternoon” (Exodus 12:6). Is it so that the whole assembly slaughters the offering? But only one person from each group slaughters it. Rather, it can be derived from here that the legal status of a person’s agent is like that of themself.
But why is the person liable? Let us say that the legal status of a person’s agent is like that of themself. The Gemara answers: There it is different, as there is no agency for transgression, as we say: When there is a conflict between the words of the Master, i.e., God, and the words of the student, i.e., a human being, whose words should be listened to? Consequently, the agent is considered to have acted of their own accord, and the one who sent the agent bears no responsibility.
With regard to damage caused by a fire lit by one person spreading to a location other than where it was lit, the Gemara cites a dispute among the amora’im: It was stated: Rabbi Yoḥanan says: The liability for damage caused by one's fire is due to its similarity to one's arrows, meaning that damage caused by a fire in a location other than where it was lit is comparable to damage caused by an arrow shot at a distant target. And Reish Lakish says: One's liability for the damage caused by one's fire is due to its similarity to one's property; one is responsible for this damage just as they are responsible for damage caused elsewhere by any of their possessions, e.g., one of their animals.
When one person brings a flame, and [then] another person brings the wood, [and a fire is started, which causes damage], the person who brought the wood is liable. When one person brings the wood, and [then] another person brings a flame, [and a fire is started, which causes damage,] the person who brought the flame is liable. If another person comes and fans the fire, they are liable. If the fire is fanned by an uncommon wind, none of them is held liable. If a person fanned a fire, but it was also fanned by the wind, the person is liable, for their [actions] caused damage. And whenever a person's [actions] cause damage, they are liable to pay for the full amount of the damages from the choicest property they own, as if the damage was inflicted directly.
MISHNA: One who sends a fire, i.e., places a burning object, in the hand of someone who his cognitively impaired or a minor is exempt for any damage later caused by the fire according to human laws but liable according to the laws of Heaven. If they sent it in the hand of a halakhically competent person, the halakhically competent person is liable, not the one who sent them.