Genèse 7:2

Pure: That will be "pure" [i.e. kosher] for Israel in the future, teaching us that Noah learned the Torah.

Seven and seven: So as to sacrifice from them-- the sacrifice upon exiting.

Of all clean cattle take thou seven by seven, male and female, and of all cattle not clean, two (and two), male and female.

הטהורה, at that time all of the pure animals [including free roaming ones] were acceptable as potential offerings to G’d.

מכל בהמה הטהורה תקח לך, as they will arrive before the ark take them inside with you. Previously, G’d had told Noach only to take the animals in pairs, one pair per species. Only now was he instructed to take 6 additional pairs of each of the species of animal known as טהורה, ritually pure. It is not clear if of the ritually impure animals Noach was to take a single pair or two pairs. How did Noach know which animals were considered ritually pure? It is possible that G’d told him which peculiarities to watch for in order that he should know which to use as an offering after the deluge. Alternately, Noach would know when he saw that some of the animals came to him in lots of seven pairs. This explanation does not suffice for the birds, seeing that apparently all the birds arrived in lots of seven pairs. We must therefore fall back on the explanation that G’d provided Noach with information how to recognise which were the ritually pure animals. In that case, we would also have to conclude that the ritually impure birds did not come to the ark in pairs of seven. What then is the meaning of the words (verse 3) גם מעוף השמים שבעה שבעה?. “also from the birds in the sky seven pairs each?” Surely, this appears to apply only to the ritually pure birds, and the word גם refers back to the word הטהורה in verse 2. If the birds generally arrived in single pairs, and the ritually pure birds arrived in lots of seven pairs, the reason was not that they be used as offerings to G’d, seeing that Noach is on record as bringing only one offering, and he would be able to bring more such offerings from the next generation of such birds if he so desired. The reason may be that G’d intended for Noach and his family to use the excess number of ritually pure birds as food without endangering any of the species’ chances of survival. G’d had already planned to permit the consumption of meat to the survivors of the deluge, something which had been forbidden to Adam at the time. Even though G’d did not withhold any kind of living creature as food for man, as we know from Genesis 9,3 כל רמש אשר הוא חי לכם יהיה לאכלה, “any moving thing which is a live will be yours to eat,” this was amended for the Jewish people who were to be a nation of holy people. It is in the nature of things that the animals described as ritually pure, טהורות, are superior as food. In the majority, gentiles do not eat the meat of the other animals unless driven to do so by hunger. Keeping this in mind, G’d ordered Noach to take more of the ritually pure animals with him into the ark, to ensure that slaughtering some of them in due course would not deplete the available supply. The principal concern was to keep these species alive, i.e. לחיות זרע, to make sure man would always find a sufficient number of these animals available for his needs. G’d, in His wisdom knew that seven pairs of each would suffice, and that the ark would be unable to accommodate more than that number, and the amount of food needed to keep them alive for a whole year.

מכל הבהמה הטהורה, “from all of the ritually pure domestic animals;” seeing that the Torah had not been given yet, and therefore there were no ritually impure domestic animals or creatures, Rashi understands the expression as referring to the domestic animals that would in the future be described as being ritually pure. We therefore learn that Noach had already studied Torah laws which had not yet been revealed publicly (B’reshit Rabbah, 40, based on Psalms 1,2) If so, why did the Talmud in tractate Zevachim folio 116 have to pose the question of how Noach knew, and to answer that the ritually pure animals came to the ark on their own, whereas Noach had to round up the others in order to bring them into the ark? According to the Talmud, Noach only recognised ritually pure animals after the event, not because he had learned the physical signs described in the Torah.
There is a third opinion according to which it became clear which animals had been ritually pure only after Noach offered some of these as offerings after having left the ark. This interpretation is also not logical as G–d had commanded him prior to entering the ark to take seven pairs each of the ritually pure animals into the ark, so that he must have known beforehand which animals to take. This is also what Rashi commented on chapter 8, verse 20. He had realised that the only reason he had been commanded to take seven pairs of the species concerned was in order to have these animals available after the deluge to serves as sacrifices. It would appear therefore that the statement that Noach had studied the Torah, must have referred to the instructions to take such ritually pure birds, (6,4) something which became clear to him when noting that these birds were monogamous, mating only with the same female. When he saw that the ark accepted more than one pair of certain animals, it became clear to him that the extra specimens must have been meant to serve as sacrifices as G–d considered them as ritually pure. “Studying Torah,” as mentioned by Rashi, must mean therefore that he learned Torah by keeping his eyes open and drawing the right conclusions. He had also noted that these animals had only kept company with members of their own species during the long months in the ark. This is most likely also the reason why, when the Torah wrote the details about the laws of chastity and forbidden sexual intercourse in Leviticus 18,23-24, it stated that Jews must not defile themselves through such animals.