Before us is Mishnah 4 in the fourth chapter of Maseches Avodah Zarah, which deals with two matters: from when does an idol take on the status of avodah zarah that is forbidden to derive benefit from, and who is qualified to nullify it and remove that prohibition from it.
"Avodah zarah shel oved kochavim asurah miyad" - the idol of a non-Jew is forbidden immediately:
The Mishnah teaches here the principle mentioned above: if a non-Jew made an image intended to serve as an object of idolatry, even though he never actually worshipped it, the very fact that he made it for that explicit purpose forbids deriving any benefit from it immediately and forever.
The source for this is the verse: "The graven images of their gods you shall burn with fire." The Torah calls them "graven images" even before they became "their gods" - teaching us that an image made for the purpose of being a god becomes forbidden to benefit from already from the moment it is made.
"V'shel Yisrael einah asurah ad shetei'aved" - and that of a Jew is not forbidden until it is worshipped:
By contrast, if a Jew made an image with the explicit intention that it serve as an object of idolatry, the image is not forbidden to benefit from until he actually worships it. Until that moment one may derive benefit from it - for example, to burn it and enjoy the light and the heat of the fire, something that will no longer be possible once benefit from it is forbidden.
"Oved kochavim mevatel avodah zarah shelo v'shel chaveiro" - a non-Jew may nullify his own idol and that of his fellow:
A non-Jew is able to nullify the status of the idolatry and strip away its sanctity. The manner of nullification will be explained in the next Mishnah, and essentially it involves breaking off part of the image. Once it has been nullified, the prohibition of benefit falls away. And this power is given to him not only regarding his own idol, but even regarding that of another non-Jew: if two non-Jews are neighbors and one of them has an idol, his fellow may come and cut off its head, and it is nullified immediately.
The version of the Bartenura:
The Bartenura had a different version of the text: not "v'shel chaveiro" (and that of his fellow) but "v'shel Yisrael" (and that of a Jew) - meaning that a non-Jew nullifies his own idol and also an image that he holds in partnership with a Jew. According to this version, if the non-Jew nullified the image, by cutting off its head or the like, the image becomes permitted even though a Jew has a share in it.
The Bartenura himself points out that even if they are partners it makes no difference, and the halachah does not follow this view: an idol belonging to a Jew, even if it is jointly owned with a non-Jew, can never be nullified and remains forbidden always. To clarify: the Bartenura understood that the Jew and the non-Jew are not partners, so that it should be possible at all to understand that the non-Jew can nullify it.
Our text, however, which is the version that Rabbi Yehudah HaNasi himself learned at a later stage of his life, is speaking of two non-Jews: one nullifies the idol of his fellow, even though he does not worship it and even though it does not belong to him at all - a non-Jew off the street who cuts off the head of his neighbor's idol.
A Jew cannot nullify:
A Jew has no power at all to nullify an idol. Not only can he not nullify an idol that he himself made and owns, which remains forbidden to derive benefit from forever, but he cannot even nullify an idol belonging to a non-Jew. A Jew never has the power of nullification in matters of idolatry, and the idol remains forbidden to derive benefit from.
"HaMevatel avodah zarah, bitel meshamshehah" - one who nullifies an idol has thereby nullified its accessories:
When a person nullifies the status of the idol itself, by cutting off its head or something similar, not only is the idol nullified and no longer forbidden to derive benefit from, but even its accessories - the items that serve it - leave the category of prohibition. A crown that rested on its head also becomes permitted to derive benefit from, since it is the crown of an idol that has been nullified.
"Bitel meshamshehah, meshamshehah mutarin v'hi asurah" - if he nullified its accessories, the accessories are permitted but the idol itself remains forbidden:
By contrast, one who nullifies only its accessories - the items are permitted while the idol itself remains in its prohibition. Removing the crown and designating it for melting down for the sake of its metal permits the crown for benefit, but the statue itself stands in its prohibition.
Understandably, if the crown is made as part of the body of the statue, then breaking the head includes the crown as well, and it is part of the nullification. But when the crown is a separate piece of metal resting on top of a stone statue, nullifying the stone structure permits the metal crown upon it, whereas nullifying only the metal crown, by melting it down, leaves the statue itself in its prohibition.
In summary: We learned in this Mishnah that an idol belonging to a non-Jew becomes forbidden to derive benefit from immediately from the moment it is made, while an idol belonging to a Jew does not become forbidden until it is actually worshipped; that a non-Jew can nullify his own idol and that of another non-Jew, while a Jew can nullify neither his own nor that of a non-Jew; and that one who nullifies the idol nullifies its accessories along with it, whereas one who nullifies only the accessories - they are permitted and the idol remains forbidden.
In the next Mishnah we will learn how nullification is carried out in practice, and what action strips a statue of its status.