1:
In the Gemara this very long mishnah is divided into four separate mishnayot. However, since in the case of most of the mishnah if one has explained one part one has explained the others it seems sensible to maintain the format which is to be found in the codices of the Mishnah.

2:
Our mishnah consists of four sections and this division is reflected in the manner in which it is presented above.

3:
Our mishnah is concerned with the extent to which a Jew may derive material benefit from an object which had been used for non-Jewish worship. For example: may a Jew buy a house which had been used for non-Jewish worship? May he benefit from a tree which was used for such purposes?

4:
If a building was originally erected to serve as a non-Jewish place of worship there is no way in which a Jew can derive material benefit from it. He may not buy it, rent it, shelter in it and so forth. However, if a building that was erected for some other purpose was renovated by non-Jews and turned into a place of non-Jewish worship a Jew may derive material benefit from the building simply by removing all the renovations that were done to make the building suitable as a place of non-Jewish worship. If all that happened was that a non-Jew brought an idol (or some other kind of non-Jewish religious symbol) into an ordinary building once the idol has been removed the building is permitted to a Jew.

5:
The next section of our mishnah follows the same pattern. If stone was originally hewn in order to erect a pedestal or altar for non-Jewish worship there is no way in which a Jew can subsequently derive material benefit from that stone. However, if the stone was erected for some other purpose and was subsequently turned into an object for non-Jewish worship (such as a pedestal for an idol or an altar) a Jew may derive material benefit from the stone after all the renovations have been removed. If all that happened was that a non-Jew took a stone and set up on it an idol (or some other kind of non-Jewish religious symbol) once the idol has been removed the stone is permitted to a Jew.

6:
The same reasoning applies to a tree. If a tree was originally planted in order to serve as an Asherah, an object connected with non-Jewish worship there is no way in which a Jew can subsequently derive material benefit from that tree. However, if non-Jews selected a some tree or other and trimmed it for religious purposes a Jew may derive material benefit from that tree once it has seen new growth which has been removed. In other words, once the tree has resumed its original shape. If all that happened was that a non-Jew chose tree and set up under it an idol (or some other kind of non-Jewish religious symbol) once the idol has been removed the tree is permitted to a Jew.

7:
The fourth and last section of our mishnah is different. In order to answer the question our mishnah asks: What is an Asherah? The Gemara [AZ 48a] rather reasonably objects: why ask such a question when previously the mishnah has explained that "there are three kinds of Asherah"? The resolution of this objection is to specify to what exactly it is referring. In our mishnah

8:
Our mishnah now brings a concrete event to illustrate the difference between the sages and Rabbi Shim'on. The incident is described as occurring in 'Zaidan'. It is, of course, very tempting to assume that the reference is to the town of Sidon which today is in Lebanon, several miles north of Nahariyya. But there is considerable evidence to suggect that the reference is, in fact, to the town of Bet Saïda (which in the Christian scriptures as called Bethsaida). This fishing town was near where the river Jordan enters the sea of Galilee in the north.

9:
The Gemara [AZ 48a] adds a practical consideration:

Rav and Shemu'el were the greatest of the Amoraïm of the first generation in Babylon (mid 3rd century CE). Amemar is a much later Amora and apparently he is quoting Rav Yehudah, a great Amora from the second or third generation.

For more information about the Asherah see AZ 042.

Since I am told that my recuperation from pneumonia will be a long haul I am going to abandon my custom of sending out these shiurim on fixed days and will send them out whenever I can.