Our Gemara on Amud Beis discusses an aspect of bird shechitta that is different from animal shechitta. According to one opinion, the shechitta remains valid even if the windpipe and gullet are uprooted, unlike with an animal.

The Gemara first suggests that this opinion also holds that the requirement of shechitta for birds is only rabbinic, therefore they were lenient in this regard. While the position that holds uprooting invalidates bird shechitta as well also holds that shechitta of birds is a Torah requirement. 

Then the Gemara rejects this assessment with the following logic. If the rabbis presumed to require shechitta by birds, whatever motivated this, should also motivate the full requirements, including that there be no uprooting. And it also is a principle that the rabbinic enactments are modeled to follow the Torah rules (see Ritva ibid.) Therefore it makes more sense to propose the opinion that holds uprooting invalidates even a bird shechitta aligns with the opinion that its shechitta is rabbinic, and the rabbis modelled its laws after the animal shechitta. On the other hand, it is more reasonable to suggest that the opinion which holds uprooting is kosher by bird shechitta is actually from Torah law. Why? Because, in any case, it is a tradition from Moshe from Sinai and so just as many details in Torah laws do not always correspond to others, so too, in Torah law a bird shechitta could be different.

Let us study the principle that this discussion revolves around: Rabbinic enactments are modeled to follow the Torah rules. Why is this true, and what is the deeper meaning? It suggests a perspective on rabbinic rules that are broader than merely enacting legislation or extensions of law to allow for social functioning or safeguarding the Torah. The Maharal (Be’er Hagolah 1:1) explains that the rabbis would build off a pre-existing sensitivity expressed by the verses but not legislated. 

His prime example is the rules of washing hands. On the surface, the law seems far-fetched: The kohanim were required to wash their hands before eating Terumah because their hands were declared rabbinically impure. Then, on top of that rabbinic prohibition, all Jews, not just Kohanim, were required to wash their hands so as not to forget the custom in non-Temple times. (See Mishna Berura 158:1.) So, we are forever required to wash our hands in order to preserve a custom amongst the priests, which was in the first place, only rabbinic?

The Maharal sees it differently. The rabbis (Chulin 106a) cite a verse as a support for washing hands. The Zav is considered impure until his disease heals and he undergoes a purification ritual. Yet the verse (Vayikra 15:11) dictates the following:

“Whomever the one with a discharge touches, without having rinsed his hands in water, shall wash their clothes, bathe in water, and remain impure until evening.”

Actually a Zav will NOT become purified by washing his hands. The rabbis see this verse as a hint to the idea of washing hands for Terumah. The Maharal explains the Torah referred to the hands as a locus of probable contamination because people are constantly in contact with things and do not realize it (Shabbos 14a). It’s not that actual purity and impurity were legislated to hands alone, but the rabbis saw the Torah as highlighting a sensitivity to this idea. Noting the sensitivity, the rabbis created a whole new series of laws regarding hand purification.

This is interesting, but one might ask, if the Torah already had a sensitivity to the hands as a vector of impurity, how come the Torah itself did not explicitly legislate this? The Maharal does not explain this but I believe the answer is as follows. There are an infinite number of ethical and moral situations that can arise so it is impossible to legislate all of them explicitly. Furthermore, aside from the impracticality of legislating all these situations, every law also boxes a person in, and no law can be flexible enough to account for every situation. Therefore, the Torah balances regulations with implied lessons that can guide even when the law does not explicitly cover it. (See a fascinating Magid Mishna, Laws of Neighbors 14:5, who elaborates on this idea.)

You might ask, if so, then why didn’t the rabbis leave it as is, an important idea or consideration without imposing a new rule? This is because they must have noticed the sensitivity and voluntary ethical drive was losing ground in that area. When you think of it this way, it turns the entire concept of rabbinic law on its head. They are not innovations but rather formalizations of what existed intuitively. According to this idea, sagely, holy people intuited the need to wash hands to maintain physical and spiritual purity since the time of Moshe. (By the way, it is for BOTH health and spiritual cleanliness, see Mishna Berura 158:1.) The rabbis only found it necessary to formally legislate after that sensitivity started to degrade. 

Similarly, perhaps the laws of Muktzah and Mimtzoh Cheftzecha (rabbinic prohibition against speaking about business and weekday pursuits on Shabbos) were observed from the time of Moshe. They were observed in the sense that people sensed the sanctity of Shabbos and voluntarily abstained from many actions that had a weekday feel to it, even including unnecessary carrying of objects not related to immediate use. People had that sensitivity in their bones as a result of a deep understanding of the will of God through the Torah. They did not need any rabbinic enactments. The rabbinic enactments only came later when they saw that people did not understand or feel that vibe anymore and it needed to be reinforced through legislation.