1:
Our mishnah is concerned with a situation where the house of a Jew shares a wall with a non-Jewish temple. If the common wall collapses and the Jew's house needs to be rebuilt the Jew may not simply restore the situation as it was, because by rebuilding the wall that they have in common he would be benefiting the non-Jewish temple, which, as we have seen, is forbidden.

2:
Of course, one could ask a rather pertinent question: when the Jew built his house in such a way that he used a wall of the temple as one of his walls was he not thereby deriving benefit from the pagan temple? The Talmud of Eretz-Israel [AZ 23a] relates to this problem and suggests that the Jew built his house first and then the organisers of a pagan temple came along and made one of the walls of the Jew's house a wall of their temple too. However, I am not at all certain that this explanation fits in with the rest of the mishnah.

3:
The solution of the Jew's problem according to our mishnah is to leave a gap between the pagan temple and his own house when he rebuilds the fallen wall. (This must be a gap of at least 4 cubits - somewhatless than 2 metres.) He must build his new wall inside his own area, so that it no longer abuts the pagan temple. However, if the wall belonged to both the Jew and the pagan temple the four cubits must be measures from what was the centre of the fallen wall - half to the temple and half to the Jew, as it were. (It is this part of our mishnah that does not accord with the explanation suggested in the Talmud of Eretz-Israel and expounded above.)

4:
The ruined wall cannot be used by the Jew because it would be impossible to determine which of the stones or the wood or the rubble belonged to the Jew and which belonged to the pagan temple.

5:
There remains also the question of what to do with the gap thus left. If the Jew leaves the gap as it is there is a possibility that when they rebuild their temple the non-Jews will utilise the extra space thus afforded. So, the Jew must use the space in some manner. The Gemara [AZ 47b] suggests that the best use for the space thus created would be to turn it into a toilet or privy. However, this raises an halakhic problem. To use the space as a toilet for the residents of the house would mean that those who use it would be doing so while exposed to other eyes, because the privy would just be a space, not a building or a shack. The Gemara now suggests that the this toilet would only be used at night. But even this solution is rejected, because the sages have said:

So, eventually the Gemara offers two solutions. The first is that the toilet be used by children only. Alternatively, the area need not be used for such bodily functions at all! The area should be strewn with thorns and brambles.

6:
The Torah [Leviticus 11:31] states:

In other words, ritual impurity is imparted from a dead reptile only when it is touched. In our mishnah the sages say that the debris of the fallen wall must be treated like a dead reptile. They derive this from the fact that dead reptiles are referred to as abhorrent and also whatever pertains to pagan ritual is described as abhorrent:

7:
Rabbi Akiva in our mishnah seeks to go further. Not only in the case of dead reptiles is the language of abhorrence used. The prophet [Isaiah 30:22] says:

Now, a menstruating woman imparts ritual impurity not just by direct touch but also by indirect contact, such as touching something she is carrying. So Rabbi Akiva is saying that the appurtenances of idolatry impart an even greater degree of ritual impurity than the degree suggested by the rest of the sages. The view of Rabbi Akiva is rejected: in an age where ritual impurity was still a major concern contact with the religious appurtenances of idolatry passed ritual impurity only to someone who directly (and deliberately) touched them.

I would like to express my sincerest thanks to all those dozens of participants who sent me their best wishes for a speedy recovery from my bout of pneumonia. I am still rather weak, but on the mend, thank God. I shall try to resume the regular shiurim, but for a time I may not have the strength to send them out as regularly as usual. Please bear with me.