"If [an egg laid on Shabbat or Yom Tov] gets accidentally mixed into a large number of other [permitted eggs], all are forbidden [until after Shabbat or Yom Tov.]" This ruling coheres well with Rabba's reason [for prohibiting an egg laid on Shabbat or Yom Tov]: that he is using [the Shabbat day] to prepare [for after Shabbat]. This is a Torah prohibition, and in cases of doubt we must be stringent. But the ruling would make no sense to Rabbi Yosef and Rabbi Yitzhak, who say that [we prohibit an egg laid on Shabbat or Yom Tov until after Shabbat or Yom Tov] Rabbinically. If this is a Rabbinic prohibition, we should rule leniently!
In the past few weeks, we have seen that there are two different types of prohibitions on Shabbat: Torah prohibitions and Rabbinic prohibitions. We have seen that there are a number of reasons why our Sages instituted prohibitions beyond those of the Torah. For instance, they prohibited a number of activities which are similar or could be confused with Torah prohibitions, acts which could lead to violations of Torah prohibitions, and acts which they deemed not in consonance with the "spirit of Shabbat." But sometimes, as is the case in our passage, there will be a disagreement in the Talmud about whether a particular prohibition devolved from the Torah or was instituted by our Sages.
In our passage, we encounter a prohibition on using an egg laid on Shabbat. The origins of this prohibition are obscure: is it a Rabbinic prohibition or a Torah prohibition? Rabbah disagrees with Rabbi Yosef and Rabbi Yitzhak about this question. Now, you might ask, "What's the difference? Either way it is prohibited, right?" The ruling that opens our passage provides the answer to that question. Since our prohibited egg got mixed up with permitted eggs, when we pull any egg out of the basket, it may or may not be the prohibited egg. If the prohibition is from Torah, the principle we follow is to be stringent and treat all the eggs as if they are prohibited. If it's a Rabbinic prohibition, then we are lenient, treating all the eggs as if they are permitted. We take the chance of violating human requirements, even those of our holy Sages, but we never risk giving offense to the Divine.
May we strive to live our lives with the deep sensitivity to the demands of Heaven even in the small details of our lives, as we see here.