How Did Noah Know What Was Clean?

In the early chapters of Genesis, God spoke to Noah about building an ark to save his family and animals. God said, “You shall take with you of every clean animal by sevens, a male and his female; and of the animals that are not clean two, a male and his female; also of the birds of the sky, by sevens, male and female, to keep offspring alive on the face of all the earth” (Genesis 7:2-3).

Question: This passage mentions clean and unclean animals taken onto the ark. Yet the distinction between clean and unclean isn’t defined in the Bible until Leviticus 11, roughly 1000 years after Noah. Therefore, what is this passage in Genesis referring to? How did Noah know what was clean and unclean? Does it mean unclean in the same way as in Leviticus, or something else? Here are six possibilities to consider and one lesson as take away.


  1. The passage in Genesis 7 may be a scribal error or insertion. This would not seem to be the case. Of the 19 commentators I consulted, none of them mentioned this as a possibility. In addition, there are other Genesis passages that give a “law” about something (Genesis 9:1-6) though the law code wasn’t fully revealed until Moses.

  2. Does this refer to a religious practice that was culturally acceptable in Noah’s day? Sacrifices for sin or favor were not unknown in the Ancient Near East (ANE). This included animals, like pigs, that were inappropriate for sacrifice. Noah may have been familiar with such rules and they were applied to the animals he brought with him. This does not mean that ancient Judaism was born out of pagan practices of the day. It simply suggests that God condescended himself to using what was acceptable during that period’s religious expression when he commanded Noah to take seven of the clean variety, rather than just two. But, this is just speculation.

  3. According to the literary theory known as the Documentary Hypothesis, this section of Genesis 7 would fall under a priestly writing in the post exilic period of the Jews. However, this is pure fantasy as the Documentary Hypothesis has been widely discredited.

  4. God revealed what was clean and unclean previously but didn’t elaborate on it in scripture. This is likely, though we don’t have direct scriptural evidence for it. However, it may be implied. In fact, there may be an indication of this in Genesis 4:2 which records that, “Abel was a keeper of flocks.” If some commentators are correct and man did not eat meat at this time, then Abel could only raise flocks for two purposes, clothing and sacrifice. Genesis 4:4 notes that Abel brought his, “Fat portions.” This indicates animal sacrifice conducted by a set of rules since Abel knew how to prepare a sacrifice. He didn’t simply kill the animal and set it ablaze. It is likely that God or his parents educated him on how to perform an acceptable sacrifice. We could say that God gave him a distinction between what was ceremonially clean and what was not so that he could make his sacrifice properly.

  5. Clean and unclean may have been known but not in the kind of detail as defined in Leviticus 11. The previous points elaborates on this a bit. This may go back to the culture of the day, but we have nothing specific to point to other than what has been uncovered from the ANE period.

  6. The clean animals were meant for sacrifice so seven was required to keep the various species alive. Several commentators have mentioned this possibility. This depends upon how often Noah and his family offered sacrifices. Certainly a frequent offering would have burnt up the available animals rather quickly. But if he sacrificed once a year, or during regular harvest and planting seasons then the need to kill fresh animals would be few in the first years of rebuilding their lives. But the scripture simply does not elaborate on this.

Our lesson? First, the Bible is not exhaustive in its claims, rather, it is sufficient in its claims. We do not need to know everything about these early days or have a concrete answer to this question in order to live a godly life. Theologically, this issue is only of tertiary importance. 

Furthermore, this is not an important issue for us today because the sacrifice of Christ is sufficient for our needs and no sacrifices for sin remains. Also, we have no biblical dietary restrictions other than not eating blood (Acts 15:20). While we can learn from this passage about God and how he dealt with early man, it is in Christ that all of these things are fulfilled and it is to him alone that we should give our full attention. Jesus was the ultimate clean sacrifice, dying for the unclean, whom he cleansed by his blood to restore us to the image of God.

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