To understand what our sages said, “whatsoever hath scales is known to have fins. And whatsoever hath fins, it is not known if it has scales.”
This means that there are two conditions in Kashrut: fins and scales. If we have scales, that’s complete Kosher and it is certain that there are fins. But if we have fins it is still not certain that it has scales and it has to be checked. It’s like the degree of Hassadim (mercy) and the degree of Hochma (wisdom), the degree of bestowal and the degree of receiving in order to bestow. If he receives in order to bestow, then he certainly bestows in order to bestow as well. But if he bestows in order to bestow, it’s still not certain that he can also receive in order to bestow...