R. Akiva says: Scripture comes to teach only the mitzvoth stated here, to forbid to them flesh of "stabbing" (nechirah [as opposed to shechitah, ritual slaughter]), and when they entered the land it was forbidden to them. R. Elazar b. Azaryah says: Scripture comes to teach you derech eretz (proper deportment), that one should eat flesh only out of desire.
I might think that he could buy meat in the marketplace and eat it; it is, therefore, written (Ibid. 21) "then you shall slaughter of your cattle and of your flocks" — One is not to eat flesh unless he has cattle and flocks (of his own). I might think that he is to slaughter all of his flocks and all of his cattle; it is, therefore, written "of your cattle," and not "all of your cattle"; "of your flocks," and not "all of your flocks."