In Gen. 7 God instructs Noah to bring the animals into the ark and tells Noah to bring 7 pairs of clean animals and 2 pairs of unclean animals. The question is, how did Noah know the difference between clean and unclean animals? The bible doesn't make any mention of clean and unclean animals until Lev. 11, but before that there is no commandment directly specifying what is clean an unclean.
Before the law to abstain from unclean food, there was a spiritual law. Noah knew this spiritual law, and it was by this wisdom he knew what God meant when he was commanded to make a separation of the animals.
Starts in Eden
When God made Adam, he allowed Adam to name all the animals on the earth, Gen. 2:19. At this point, there was no separation between clean and unclean animals. The commandment God gave Adam was the Law, and at this point God only made a distinction between obedience and disobedience.
Disobedience, which is the fruit of the knowledge of good and evil (Earth's carnal wisdom) which is death (2 Cor. 3:6), and obedience which is the tree of life which (God's promise of eternal life through obedience ,believing Jesus is the son of God, Galatians 6:8).
Seeds are the words you receive (Matthew 13:19), and the fruit is the works (Matthew 13:23). Works come by faith in what you believe (James 2). Their is either faith in God's truth which brings good works, or faith in another doctrines that leads to bad works (Matthew 3:8,10).
God's commandment brought separation to the fruit in the garden, this separation is deeper than the surface. The spiritual meaning of this commandment carries a greater weight, the good fruit is the good works that come as you obey God, and the bad fruit is the bad works that comes as you disobey God.
Separating the animals
The Devil appeared in the form of a serpent in the garden (Gen. 3:1), which is the first time a specific animal is mentioned. The simple fact that the serpent has a name clearly reveals Adam must have named it first. But why was the serpent in the garden to begin with? Because God didn't make it a law to separate the clean from the unclean yet.
Liberty of Choice
Before the serpent was deemed unclean by the law, the Spirit gave Adam the discernment to recognize it as a threat. Hebrews 4:12 says "For the word of God is quick, and powerful, and sharper than any twoedged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart." God gave Adam his word instructing him what fruit to abstain from (Gen. 2:17-18) including the punishment for disobeying, not Eve. It was the word of God that was in Adam that gave Adam the discernment to know Satan's intentions.
God's word is described as a discerner of "the thoughts and intents of the heart" and by Adam possessing God's word in his heart, he was given the ability to discern intentions. But this ability was not in Eve because she was weak in the word of God, revealed when she misquoted God's word, Gen 3:3 "Ye shall not eat of it, neither shall ye touch it, lest ye die.". Eve added a commandment, "neither shall ye touch it..." and because there is only power in the truth, Satan was able to get the upper hand. The word makes it clear, we are not permitted to add to God's word, Rev 22:18, Gal 1:7-9.
Adam had the discernment need to know the intentions of the serpent. The serpent's presence in the garden reveals Adam tolerated Satan being in the garden. Adam knew better, but didn't do better and the result was death. This should add some light to the following verses; 1 Corinthians 10:23 "...all things are lawful for me, but all things edify not", Luke 17:10 "We are unprofitable servants. We have done that which was our duty to do.".
Seeds of Rebellion
After Satan deceives Eve and both her and Adam eat from the forbidden tree, God gives specific curses (Not in order). Adam was God's fruit in the Earth. God's word was the seed that planted Adam in the Earth and formed him, then His Spirit gave the increase which is the breath of life. Eve rebelled against God, and we know this grieves the Holy Spirit (Ephesians 4:30 "grieve not the holy Spirit of God" & Gen. 6:6 "And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually. 6 And it repented the Lord that he had made man on the earth, and it grieved him at his heart."). God's response was to multiply the woman's grievance during child birth, Gen. 3:16.
Adam received the word from Eve which Satan gave her. This seed took root in Adam and the fruit was rebellion. God curses the Earth and makes it produce thorn's and thistles (Gen. 3:18), this is because Adam's rebellion in the garden planted spiritual thorns and thistles in God's perfect garden. This disobedience defiled God's perfection. God curses Adam to toil in hard labor to get increase (Gen. 3:19). This is because when Adam planted spiritual thorns and thistles in God's garden, he defiled God's labor and time that was spent when God created it. So God defiled Adam's time through ending his life with death and God defiled Adam's labor by making him work hard for increase.
Satan was cursed above all for planting his seeds of witchcraft in God's garden (Matthew 13:25-30).
But what about Noah?
Now back to the question at hand, how did Noah know what was clean and unclean? Because Noah knew what happened in the garden of Eden and had the wisdom needed to know the spiritual implications of clean and unclean animals and fruit.
So far, we've already seen through God's word that fruit is a spiritually referring to works, either good or bad. So what about animals?
Satan was manifested as a serpent in the garden, and when God cursed Satan, God's word (the law) defined the first unclean animal. But does this specification only apply to the devils and unclean spirits? No, it apples to all peoples and spirits in the bible. Every place in scripture you read about an animal, bug, or bird, the bible is describing a spirit. And if that animal is already deemed unclean by the law, then it's describing an unclean spirit. Let me explain.
In God's own words
Jesus lays the foundation of this truth. Matthew 15:11-20 "Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth, this defileth a man." Jesus makes it clear, food has never defiled a man, making clear the bible has always referred to a spiritual implication. This is why Jesus says not to throw your pearls before swine in Matthew 7:6, the swine Jesus is talking about is people that are spiritual pigs. In Mark 7:24-30, Jesus calls the Syrophoenician woman a dog, referring to a spiritual dog. And in Matthew 12:34, Jesus calls the Pharisees vipers, again referring to a person who is a spiritual viper. All of these people are compared to unclean animals because they are spiritually unclean.
Watch what you eat
God's word makes it clear, the words you hear are eaten by your spiritual mouth Job 12:11 "Doth not the ear try words? and the mouth taste his meat?" And you become defiled when you consume words from these spiritually unclean people. Isaiah 33:15 Describes the response of a righteous person; "He that walketh righteously, and speaketh uprightly; he that despiseth the gain of oppressions, that shaketh his hands from holding of bribes, that stoppeth his ears from hearing of blood, and shutteth his eyes from seeing evil;". Ultimately, this is why we need to watch what we say because it testifies of what we eat. 1 Peter 1:15 "but as he which hath called you is holy, so be ye holy in all manner of conversation".
And this all ties together when we read 1 Corinthians 5:11-13 "But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolator, or a railer, or a drunkard, or an extortioner; with such an one no not to eat. 12 For what have I to do to judge them also that are without? do not ye judge them that are within? 13 But them that are without God judgeth. Therefore put away from among yourselves that wicked person." People who are not in Christ can only produce defiled meat. They look at the world from their blinded eyes and don't see things how they really are. This is why we're called to live separated from them, because "consuming" enough of this defiled meat defiles your own temple. You eat another's food when you begin to believe the things they say and begin to share in their same views, for other brothers and sisters, our faith in Christ strengthens eachother, but the lost simply sow doubt.
Noah knew this truth and lived his life according to it, it was his faith in God's word that was his righteousness Gen. 7:1, and what followed was insight into the spiritual world. This spiritual wisdom translated into the Earthly wisdom needed to make the separation God requested of him.
I pray this teaching is a blessing and I hope it gives you deeper insight into the Word of God!