Bereishit 8:20 Noach built an alter to G-d. He took of all the clean domestic animals and of all the clean birds, and he sacrificed burnt offerings on the altar.
After Noach had completed the evacuation of the ark, and had arranged all things in their proper places, he began to think: "Why did G-d command me to bring seven of each kosher (clean) creature into the ark? If it was only to replenish the world, a single pair would be enough. G-d's command indicates that He wishes that I offer some of them as a sacrifice. (Bereishit Rabbah 34).
He also learned this in another way. At first the kosher animals came just like the others, a single pair. Then G-d told Noach to bring an additional six pair of each kosher species into the ark. These he was to bring in personally, with his own hands. Noach deduced that G-d intended that eh should bring these additional ones as sacrifices. G-d had therefore commanded him to bring them in with his own hands, that he have a portion in preparing for this important act. (RaMBaN on Bereishit 7:8) Noach's sacrifice to G-d impacted on all of mankind. HaShem gave His blessing to mankind after Noach's sacrifice.
Based on these first seven verses of Bereishit 9, is the existence of seven fundamental laws that apply to all humanity. These laws are called "Sheva Mitzvot B'nei Noach" - seven commandments given to the descendants of Noah.
Rabbi Joseph Hertz, in his commentary on the bible, suggests that these laws constitute what might be called "natural religion," because they are essential to the existence of human society. These seven laws, in effect, constitute the Torah's concept of the minimal laws of civilization and humanity.
These laws are:
1. The establishment of courts of justice
2. The prohibition of blasphemy
3. The prohibition of idolatry
4. The prohibition of incest, adultery and other illicit sexual behavior
5. The prohibition of perception
6. The prohibition of robbery
7. The prohibition of eating flesh cut from a living animal
The seven laws teach that all of humankind must set up courts of justice and establish laws governing civil and commercial life.
Idolatry is prohibited because there must be no more than a single source of ethical truth for humankind. It is not so much the prohibition of worshiping idols, such as the sun, the moon or stones that is the issue, it is the need to recognize one G-d who established inviolate moral principles for all.
Blasphemy does not only mean not cursing G-d. It is any act that might prevent any person from worshiping in a monotheistic manner.
The prohibition of incest and adultery is essential to assure the sanctity of the human family, which is the basis of societal structure.
The prohibition of murder assures the sanctity of human life.
The prohibition of robbery assures the sanctity of property.
Tearing a limb from a living animal and eating it is one of the greatest barbarisms that can be afflicted upon an animal. If it were freely permitted, people would become even more cruel than they might be naturally.
Another remarkable, though uncomfortable, conclusion emanates from the fact that the seven Noachide principles truly represent the minimal acceptable standards for human behavior. Consequently, it is impossible to ignore the conclusion that there is a point where human beings lose their privilege to be considered "human beings" if they fail to abide by at least these seven Noachide principles.
[MeAm Lo'ez, Rabbi Bachya]