Here is the explanation that I have been considering. For now I am assuming that the sons of God are angels, that the sin of the sons of God was when these angels copulated with human women and, finally, the offspring of this sinful union were genetically corrupted fleshly beings called Nephilim. In some sense, the Nephilim were evil incarnate, fleshly beings fathered by wicked angels. This background is covered in great detail in the book by Dr. Michael S. Heiser, The Unseen Realm, published by Lexham Press in 2015. Dr. Heiser presents a scholarly explanation of the spiritual worldview underscored by Genesis 6:1-4 and how it influenced much of the rest of scripture. Dr. Heiser is also the resident scholar for Logos bible software fir any on this blog use Logos. One key issue regarding the sin of the sons of God explanation described above or the "Sethite theory" is that according to Genesis 6:4, the sin of the sons of God occurred both in the days before the flood and also afterwards. In other words, the flood did not resolve or put an end to the “sin of the sons of God” described in Genesis 6 verses 1, 2, and 4. Now it came about, when men began to multiply on the face of the land, and daughters were born to them, that the sons of God saw that the daughters of men were beautiful; and they took wives for themselves, whomever they chose…The Nephilim were on the earth in those days, and also afterward when the sons of God came in to the daughters of men, and they bore children to them. Those were the mighty men who were of old, men of renown. Nephilim existing “also afterwards” is problematic because the intent of chapters 7 and 8 is to convey that no flesh was left alive. Genesis details the flood covering the mountains for 150 days with Noah in the ark for over a year to emphasize that all flesh living in those days died. The water prevailed more and more upon the earth, so that all the high mountains everywhere under the heavens were covered. The water prevailed fifteen cubits higher, and the mountains were covered. All flesh that moved on the earth perished, birds and cattle and beasts and every swarming thing that swarms upon the earth, and all mankind; of all that was on the dry land, all in whose nostrils was the breath of the spirit of life, died. Thus, He blotted out every living thing that was upon the face of the land, from man to animals to creeping things and to birds of the sky, and they were blotted out from the earth; and only Noah was left, together with those that were with him in the ark. The water prevailed upon the earth one hundred and fifty days. The idea being conveyed is that, except for Noah and his family, all of the human descendants of Cain or Seth perished as well as all the Nephilim, the corrupted flesh resulting from the sinful union of women with wicked angels. In other words, the passage is trying to convey that none of those living in Genesis 6 made it through alive to Genesis 9 except Noah’s family. In contrast, Noah was pure in his flesh and not genetically contaminated by the sin of the sons of God. He is referred to as having integrity or being perfect “in his generations” in both Genesis 6:9 and 7:1. Now here is the problem, the Nephilim reappear after the flood and their descendants are described as living in the region of Canaan from Genesis 14 through to 1 Chronicles 20. In Numbers 13:31-33, the spies Moses sent into Canaan describe the Nephilim they found living there. This passage clearly describes the “sons of Anak” as descendants of post-flood Nephilim living in Canaan immediately after Sinai and Israel’s exodus from Egypt. But the men who had gone up with him said, “We are not able to go up against the people, for they are too strong for us.” So they gave out to the sons of Israel a bad report of the land which they had spied out, saying, “The land through which we have gone, in spying it out, is a land that devours its inhabitants; and all the people whom we saw in it are men of great size. There also we saw the Nephilim (the sons of Anak are part of the Nephilim); and we became like grasshoppers in our own sight, and so we were in their sight.” Because all the pre-flood Nephilim perished in the flood, this means that the sons of God (angels) actually continued to sin and copulate with women after the flood, creating new Nephilim. Regarding the "Sethite theory," there were only Noah's descendants, Sethites, the descendants of sinful Cain had all perished in the flood. Thus, Anak’s father, Arba, mentioned in Joshua 15:13, was either a wicked angel himself or the son of a wicked angel. In other words, the flood did not resolve the problem of the sin of the sons of God. In addition, the passage in Numbers is not the only scripture that refers to Nephilim present after the flood. Clans of Rephaim named in Genesis 14:5-7, are described in greater detail as Nephilim in Deuteronomy 2:10-11 and 3:11-13 when scripture explains the early history of Moab and Edom. In short, as seen in the passage below, the Anakim (sons of Anak) and Rephaim were both Nephilim descended from wicked angels and living in Canaan. The Emim lived there formerly, a people as great, numerous, and tall as the Anakim. Like the Anakim, they are also regarded as Rephaim, but the Moabites call them Emim. Joshua mentions Nephilim often in the conquest of Canaan in Joshua 12:4, 13:12, 14:12-15, 17:15 and Judges repeats the story in 1:20. King David battles Nephilim beginning with Goliath and ending with 1 Chronicles 20:4-8 that documents their final destruction during his reign. The Hebrew term for giants in these verses in Chronicles is Raphah, a form of Rephaim, and linked to the Nephilim. The bottom line is that the existence of post-flood Nephilim is significant in the history of Israel up through the kingdom of David. Moreover, after the Nephilim’s descendants are exterminated by David and his men, they disappear from the narrative of the Old Testament; they become extinct in the biblical record. So why then and not now? What happened to prevent the sin of the sons of God from infecting the earth and humanity with incarnate evil? Why do we only find the descendants of Nephilim, like the sons of Anak, after Sinai? I believe the answer is found in Genesis 6:3 within the context where the sin is first described. It seems as if the statement made in Genesis 6:3 is God’s decree of judgment to resolve the sin of wicked angels corrupting flesh described in Genesis 6:11,12. Noah alone was found to be both righteous and have integrity in his generations, free from the genetic corruption of wicked angels. Here is God’s decree: Then the LORD said, “My Spirit shall not strive with man forever, because he also is flesh; nevertheless his days shall be one hundred and twenty years.” At the time God made this decree, humans lived many hundreds of years; Noah lived 950 years. Immediately after this decree and beginning with Noah’s sons, the lifespan of men began to decline. The “lifespan genealogies” of Genesis are unique in scripture, documenting the lifespan of every father from Adam to Moses in each generation. Remarkably, Moses is the first man recorded to live exactly 120 years and after Moses the lifespans of his sons are not recorded. Their mission accomplished; the lifespan genealogies end with Moses as illustrated below. Age Man Reference 930 Adam Gen 5 912 Seth Gen 5 905 Enosh Gen 5 910 Kenan Gen 5 895 Mahalalel Gen 5 962 Jared Gen 5 365 Enoch Gen 5 (did not die) 969 Methuselah Gen 5 777 Lamech Gen 5 950 Noah Gen 9, 11 600 Shem Gen 11 438 Apachshad Gen 11 420 Shelah Gen 11 464 Eber Gen 11 239 Peleg Gen 11 239 Rue Gen 11 230 Serug Gen 11 148 Nahor Gen 11 205 Terah Gen 11 175 Abraham Gen 25:7 180 Isaac Gen 35:28 147 Jacob Gen 47:28 137 Levi Ex 6:16 133 Kohath Ex 6:18 137 Amram Ex 6:20 120 Moses Deut 34:7 If God’s judgment on the sons of God recorded in Genesis 6:3 means that the sin of the sons of God would cease when the lifespan of a man reached 120 years, then we would expect this to happen during the lifetime of Moses. It seems this is exactly what we find in scripture. After Moses, the sin of the sons of God ceased. After Sinai wicked angels no longer father new Nephilim. Only their “sin incarnate” corrupted descendants remained on earth to be exterminated. This same distancing of spirit from humans occurs with God and good spirits. Exodus culminates when God came down on Mt Sinai and met directly with His people, speaking His ten commandments to them in His own voice from the burning fire on the mountain. The people could not stand this tangible presence of God and declared they would die if it continued. God agreed with them. To speak to His people God implemented mediators, first Moses and then the prophets after him Numbers 12:6 Deuteronomy 18:15-22. Moses, unlike the prophets who followed him, knew God tangibly Deuteronomy 34:10 like Abraham, Noah and Enoch who all lived more than 120 years. These words the LORD spoke to all your assembly at the mountain from the midst of the fire, of the cloud and of the thick gloom, with a great voice, and He added no more. He wrote them on two tablets of stone and gave them to me. And when you heard the voice from the midst of the darkness, while the mountain was burning with fire, you came near to me, all the heads of your tribes and your elders. You said, “Behold, the LORD our God has shown us His glory and His greatness, and we have heard His voice from the midst of the fire; we have seen today that God speaks with man, yet he lives. Now then why should we die? For this great fire will consume us; if we hear the voice of the LORD our God any longer, then we will die. For who is there of all flesh who has heard the voice of the living God speaking from the midst of the fire, as we have, and lived? Go near and hear all that the LORD our God says; then speak to us all that the LORD our God speaks to you, and we will hear and do it.” The LORD heard the voice of your words when you spoke to me, and the LORD said to me, “I have heard the voice of the words of this people which they have spoken to you. They have done well in all that they have spoken.” Scripture does not explicitly state how a 120-year lifespan actually stopped the sin of the sons of God, it simply ceased during the life of Moses. I believe, however, that the shortened lifespans are a clue that a genetic decay happened in humanity such that when the lifespan declined to 120 years, spirits (good or bad) were no longer tangible but became less physical to our human bodies. Now for the sin of the sons of God to occur, spirits have to be tangible in ways that our current bodies no longer genetically tolerate. In early Genesis spirits appear physical, God walks with Adam and Eve Genesis 3:8. Adam sees the Cherubim with flaming swords guarding Eden Genesis 3:24. God meets Cain and proclaims His judgment Genesis 4:9-16. God physically walks with Enoch and Noah Genesis 5:22, 6:9. God and two angels meet and dine with Abraham Genesis 18:1-33. The two angels dine with Lot Genesis 19:3 and wicked men of Sodom (allies of the Nephilim Genesis 14:1-9) attempt to physically assault angels echoing of the sin of the sons of God Genesis 19:5. Spirits physically grab Lot and his family to lead them out of Sodom Genesis 19:16. Jacob wrestles with an angel Genesis 32:24-32. In those days God and spirits can be tangible. After Moses, spirits interact with the physical world but are more distant physically. The angel that spoke with Gideon burned up the dinner that Gideon had brought him instead of eating it Judges 6:21 and the same is true for Sampson’s parents in Judges 13:16. The only angelic “touching” happens to people in visions like Isaiah Isaiah 6:7 or Jeremiah Jeremiah 1:9 or during their sleep as when the angel touched the sleeping Elijah 1 Kings 19:5-7 or when the angel grabbed the sleeping Peter in his prison cell Acts12:7 or even touched Daniel in both visions/sleep Daniel 10:9-21. After Moses, the “touching” by spirits is always linked to visions/dreams/or sleeping and not wakeful activity as seen earlier in Genesis. In conclusion, it seems that the means God used to stop the sin of the sons of God was linked to the 120-year lifespan decreed in Genesis 6:3. While wicked angels continued to sin with women and create new Nephilim after the flood; the sin of the sons of God finally ceased with Moses at Sinai in Exodus 20. Spirits, both good and bad, became less physical. After Moses died at 120 years old, only wicked descendants of the Nephilim remained on earth and these were destroyed by God’s people as they conquered Canaan. Let me contrast the physical interaction between humans and spirits before and after Moses another and even stronger way. In Genesis 18 God and two angels visit Abraham who invites them to dinner and they dine with him Genesis 18:8. In Genesis 19 the two angels visit Lot and dine with him Genesis 19:3 and they physically grab Lot and his family to drag them out of Sodom Genesis 19:16. Even more dramatic is Genesis 32:24-32 where Jacob wrestles with angel as confirmed in Hosea 12:4. It is very clear that spirits can eat with, physically grab and even wrestle humans before Moses. After Moses, during a dramatic event in Jerusalem in Luke 24:36-43, we find Jesus seeking to prove to His disciples that He is a resurrected man and not a spirit. Jesus tells the apostles, “Touch Me and see, for a spirit does not have flesh and bones as you see that I have.” Jesus Himself claims that spirits are not tangible with flesh and bones to be felt at that time. When they still did not believe Jesus then goes further to prove He is not a spirit by asking for something to eat, implying that spirits do not eat food. This is consistent with the two angels that simply burned the meals offered to them after Moses Judges 6:21, 13:16. After Moses, spirits do not eat or touch humans except in dreams, sleep or visions. The decree of Genesis 6:3 implemented with Moses seems to be the best explanation to reconcile the certain evolution of spirit/human interaction from where spirits touch and eat to where they neither touch nor eat.