daf bit: Chagigah 10

[cellio]

The mishna says: the laws concerning the dissolution of vows "hover in the air and have naught to rest on" -- meaning they have lack scriptural support. And the laws of Shabbat, festival offerings, and acts of trespass have "scant support but many laws". And the laws of civil cases, temple offerings, Levitical purity, and forbidden relations have what to rest on, and it is they that are the essentials of the torah. The g'mara then goes on to dispute claims that some laws have little or nothing to stand on; the rabbis find torah support for all of these laws, even if some are not stated as explicitly as others. (10a-b)

It certainly seems (though I haven't done the counting) that this last set gets a lot more explicit detail in torah. We understand the laws of forbidden work on Shabbat, for example, from the fact that the torah says "don't work on Shabbat" and then talks about building the mishkan, so the rabbis conclude that the things you need to do to build the mishkan are forbidden work. Laws about civil damages, who can marry whom, and what offerings to bring are, on the other hand, spelled out in detail.

(Lest you think that this is because if the torah spells it out then the rabbis don't need to -- no, these other laws are expounded and detailed in the oral law, too. The oral law supplies details of how to follow the laws given in the torah.)