Genèse 6:19

And of all that liveth of all flesh, two of every (kind) shall go into the ark, to be preserved alive with thee: male and female shall they be.

OF ALL FLESH. It is known that there are a great many beasts, and some of them — such as elephants, rams and others — are very large; likewise, the creeping things upon the earth are very many. Of the fowl of the heaven there are also innumerably many kinds, just as our Rabbis have said: “There are one hundred and twenty kinds of unclean birds in the east, and all of them belong to the species of ayah (kite).” Clean fowl are innumerable. Noah was thus obligated to bring all of them into the ark in order that they may beget their like. If you would gather a full year’s supply of food for all of them, [you would find] that this ark and ten others like it could not hold it! But this was a miracle of a small space containing a great quantity. And in case you suppose that he should have made it [the ark] very small and rely on this miracle, the answer is that the Holy One, blessed be He, saw fit to make it large so that the people of his generation should see it, wonder at it, converse about it, and speak of the subject of the flood and the gathering of the cattle, beast, and fowl into it so that perhaps they would repent. Furthermore, he made it large in order to reduce the miracle for such is the way with all miracles in the Torah or in the Prophets: whatever is humanly possible is done, with the balance left to Heaven. Now be not persuaded to say as Ibn Ezra that the three hundred cubits [of the length of the ark were measured] in cubits of a man like Noah, who was unusually tall. If so, the other people were also tall, and the beasts and fowl of those generations were also tall until the world was struck by the flood! Moreover, the cubits here are the standard cubits of the Torah.

THOU SHALT BRING INTO THE ARK, TO KEEP THEM ALIVE WITH THEE. G-d thus commanded Noah that he concern himself with and help them in their entering the ark and that he strive on behalf of their existence even as he would for his own life.

ומכל החי מכל בשר, a reference to the living creatures on the dry land only.

שנים מכל, Noach was told that these animals were to be admitted in pairs. G’d specified further, זכר ונקבה יהיו.. תביא אל התבה, after the animals which came of their own accord had been accommodated in the ark. What prompted some of these animals to come to Noach’s ark on their own? They were inspired by the same kind of imagination which unerringly enables them to find grazing land etc. G’d, no doubt, aided their imagination in this instance.

להחיות אתך, to keep them alive with you by feeding them on a daily basis.

ומכל החי....תביא, “and bring from all living species, etc.” According to Rashi the wording includes species of demons. In B’reshit Rabbah 31,13 Rabbi Aushiyah claims that the oblique wording of the Torah was exploited by disembodied spirits to demand entrance to the ARK. Noach refused them entry until they could appear with their partners. He used the fact that the Torah added the words מכל בשר, “from all that is flesh,” to deny entrance. Another version is that “Lie” begged for entry into the ark. When Noach heard this he demanded that “Lie” come with its partner. “Lie” chose the spiritual representative of all thieves as his partner. When this arch thief asked “Lie” what it would give him for appearing before Noach as its mate, “Lie” answered that it would give him everything it acquired through falsehood. They therefore entered the ark side by side. This is the origin of the well known proverb: “whatever is sown by falsehood is reaped by thievery.” A different version quotes Noach as tying that pair to the outside of the ark without permitting it to enter it. [Rashi, i.e. the author of the Midrash, was probably forced to give such an interpretation as we might have thought that if all living creatures died except for Noach and his family, how come there was still falsehood and thievery on earth even after the deluge. Ed.]