While lighting Shabbat candles is a rabbinic obligation, the Sages remained concerned lest the proximity to a burning candle might lead to prohibited actions of kindling or extinguishing the flame. The fundamental dispute in the Mishna on today’s daf is with regard to the determination whether or not indirect acts of kindling and extinguishing fall within the parameters of the prohibition on Shabbat. The Mishna teaches:
A person may not pierce a hole in an eggshell and fill it with oil, and place it over the mouth of a lamp so that the egg will drip additional oil into the lamp and thereby extend the time that it burns. And this is the ruling even if it is not an actual egg but an earthenware vessel. And Rabbi Yehuda permits doing so. However, if the craftsman, who crafts ceramic vessels, attached the egg to the lamp from the outset, one is permitted to fill it with oil because it constitutes a single, large vessel. The Rabbis decreed that a person may not fill a bowl with oil, and place it beside the lamp, and place the unlit head of the wick into the bowl so that it draws additional oil from the bowl and thereby extend the time that the lamp burns. And Rabbi Yehuda permits doing so.
In the Babylonian Talmud, the rationale for this halakha is the concern lest one come to use the additional oil. However, in the Jerusalem Talmud, the Sages questioned this reason and offer a different one in its place. Only in the case of an oil lamp with a wick can one claim that the burning of each and every drop of oil began before Shabbat and is merely continuing on Shabbat. However, oil added from an eggshell or from an additional vessel will only reach the wick on Shabbat itself. It will only begin burning then, which is tantamount to having been lit on Shabbat.