How do non-Jews know that HaShem commands them to follow the Noahide laws? What is the source for the Seven Commandments of the Noachides?
The seven Noahide laws are the most basic and minimal moral obligations of mankind, and were always around as common knowledge instilled by God in nature and by commandment (according to tradition: 6 to Adam and the 7th, prohibiting live meat- to Noah), meant to be observed by gentiles as seen throughout the book of Breishit/Genesis, way before the giving of the Torah to the Jews on Mt. Sinai. 1. IDOLATRY- was always basic logic and the most minimal morality and respect for the One and Only God [regarding the important connection between monotheism and basic morality, see the bottom paragraphs below, reprinted from a previous question.]. Accordingly, Ya’akov/Jacob commands his entire entourage (which clearly included gentiles, see 35, 8) upon entering the Holy Land, “remove all foreign gods from among you”, 35, 2-4. Similarly, God refers to the ten plagues He brings “upon all of the [fake] gods of Egypt”, Shmot/Exodus 12, 12. 2. MURDER- Cain murdering Abel was severely punished, ch. 4; and “whoever sheds man’s blood, his blood shall be shed, for man was created in the image of God”, 9, 6. 3. ILLICIT SEXUAL RELATIONS prohibiting taking married women from others by force: see what caused the Flood: Breishit 6, 2 bemoaning the fact that the bullies were randomly taking women “whoever they desired”, and “all flesh had corrupted its ways upon the earth”, ibid, 12; Pharaoh taking Sarah and being punished, ibid, 12; Abimelech taking Sarah ibid, ch. 20 and Rivka ch. 26, being threatened by God if they don’t return those wives of others. Similarly, the evil of Sodom and Amorah and their subsequent destruction revolves around such banned relations, see 19, 5-8; and Lot is seen disgraced for sleeping with his daughters who had to get him drunk in order to do so, ch. 19. 4. NOT EATING MEAT TORN FROM A LIVE ANIMAL- When Noah is allowed to eat meat after the Flood, he is commanded, “but you may not eat flesh with its life, which is its blood”, 9, 4. 5. JUSTICE systems to prevent violence - 6, 13; Abraham, the “father of many nations” (17, 5) including gentiles, teaches that “the way of God [is] to do justice and judgement”, 18, 19; and even “debates” God regarding how surely the Judge of all judges must do justice, 18, 25; the evil of Sodom “accuse” Lot of judging them, 19, 9; the story of Shechem why the entire city was punished for not bringing the governor’s son to trial for kidnapping and rape of Dinah, ch. 34. 6. THEFT- Adam and Eve had to be allowed to eat from almost all the trees because it didn’t belong to them, 2, 6; and conversely, the Flood in the time of Noach was a punishment for “hamas” [=corruption/violence] 6, 11-13 including taking that which doesn’t belong to you, 6, 2; Avraham rebukes Abimelech and his people for stealing the wells, 21, 25; Ya’akov takes for granted in his agreement with Lavan that even he knows that theft is illegal, 30, 32; and 31, 30. 7. NOT CURSING GOD- was always basic logic and the most minimal of respect for God (even if you’re not sure He exists, at least don’t curse Him! See below); as seen when the son of the Egyptian man “blasphemed and cursed the name of God” and was punished severely, Vayikra/Leviticus 24, 11. In addition, the unique wording of the prohibition repeating twice “ish ish“, “[every single, or literally:] “man, man” [not just “Jew, Jew” or “you, you”] to include gentiles, shall not curse God, ibid, 15. The severity of trying to curse God is so extreme that in most places, the term used in the Bible itself is usually the euphemistic “bless” (Kings I 21, 10-13), even regarding Job who according to mainstream Jewish tradition, was not Jewish and lived before the giving of the Torah (1, 5-11; 2, 5-9). In short, we see that way before the Torah was given to Israel, already Adam, Cain, Noah’s peers, the Canaanites, Egyptians, Philistines, Chivites, Job and mankind in general, were all expected to observe these 7 basic tenets of human morality. Unfortunately, they often weren’t observed, and it was necessary for Israel, the “light among the nations”, to strengthen this message of monotheism and morality through the Torah, since its reception. REGARDING MONOTHEISM & MORALITY, PAGANISM AND IMMORALITY- We see in the Bible, as well as archeological finds, that paganism was inevitably connected with immorality. It’s not a coincidence that the epitome of idolatrous religiosity was human sacrifice! Because as soon as you have 2 gods, inevitably they’ll be fighting with each other, because each wants to be “king of the hill”. The problem with that, is that all religions emulate their gods (“imitateo dei”), so their followers will also justify their constant fighting. In addition, as soon as you have 2 gods, that infers that each of them is lacking something. That’s why mythology is comprised of the gods taking and fighting to sieze that which they lack. In short, their gods are “Takers”, and that’s who pagans emulate and “idolize”. In contrast by monotheism, we believe in 1 God who, by definition, is perfect, and lacks nothing. Our “imitateo dei” is to emulate a God who is a “Giver”, not a “Taker”. Giving is at the top of our monotheistic agenda, and isn’t at all on the pagan program. In other words, the idolatrous world isn’t “innocent”. Polytheism isn’t just a “mathematical” problem (are there 2 or 20 gods instead of 1), but it’s a moral (!) problem. When Avraham was told to go to Israel and build a moral and just model nation to influence the rest of the world (e.g. Breishit 18, 19), and bring blessing to all mankind (ibid 12, 3), it was totally antithetical (opposite) to the violence of the accepted pagan practice, where it was accepted to murder one's wife, children and slave (and how much more so, to kill us foreigners!). This all changed with Akeidat Yitzchak where God dramatically commands: "Don't lay a finger on your son. No more human sacrifices!".