1:
As we have previously mentioned, sometimes farmers would set light to their stacks to clear the ground for the next sowing. In his commentary on our mishnah Rambam (basing himself on the Gemara, BK 61b) understands the first clause as referring to one stack being set on fire and the fire then catches on to another stack belonging to someone else. This makes obvious sense since no one would be compensated for setting light to his own stack. Remember, as we have previously explained, that farmers were wont to move all their reaped produce into one common field where each farmer was allocated a space for his produce. Presumably, sometimes the stacks were too close to each other.
2:
It seems that farmers, for convenience, sometimes would leave in (or perhaps on) their stacks the tools that were needed - spades, rakes, ladders and so forth. In the first clause of our mishnah Rabbi Yehudah is of the opinion that if a stack is set alight and the tools that are in it (or on it) are burned that the person who started the blaze must pay not only for the produce that was burned but also for the tools that were burned with it. However, the rest of the sages disagree: people don't usually leave their tools in such a manner, but remove them for safe keeping. So the compensation should only be for the produce that was burned. In this matter halakhah follows the opinion of the sages and not that of Rabbi Yehudah.
3:
Let's imagine a situation in which David sets light to his stack which, unfortunately, spreads to Sara's neighbouring stack. Worse, Sara's shepherd had tied a goat to the stack to prevent it from roaming and the shepherd was taking a rest nearby: both the goat and the shepherd are burned to death. According to the understanding of our mishnah in the Gemara [BK 61b] David must recompense Sara for the loss of her produce and for the loss of her goat, but he is not liable concerning the shepherd on the assumption that there was nothing to prevent the man from running away from the blaze.
4:
However, if the situation is reversed the law is different. If it is the shepherd who was tied to the stack then David is directly responsible for the man's death and all that ensues from that situation; so he is excused the lesser claim of monetary compensation. Clearly, the purpose of our mishnah is to establish that the ability of human beings to escape a conflagration has a direct bearing on the nature of the liability of the arsonist.
5:
The last clause of our mishnah returns us to the first clause. You will recall that Rabbi Yehudah was of the opinion that anyone who sets fire to someone else's property is liable for all the damage thus created, including its contents. The sages disagreed, because people do not usually leave their belongings in such a situation. However, they agree with Rabbi Yehudah that if the arsonist sets fire to someone's house he is liable not only for the value of the house but also for the total value of everything that was in it because people do, of course, have their belongings in their home.
