There were Giants on the earth... The Nephilim.

The increasingly popular interpretation of the following passage is that it relates a story of angels interbreeding with the human race, and that this was a primary reason for God destroying most of humanity with the great flood.
First of all, it should be pointed out that angels are not humans, they are quite different creations of God. Satan and the other angels are spirit beings, and simply cannot have physical offspring (children). They do not marry (Matt. 22:30, Mark 12:25), they are incapable of procreation, and so are genderless creatures.
Let’s look at this passage in an attempt to shed some light:

Gen 6:1 And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,
Gen 6:2 That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
Gen 6:3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
Gen 6:4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
Gen 6:5 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.
Gen 6:6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
Gen 6:7 And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.
Gen 6:8 But Noah found grace in the eyes of the LORD.

So now let’s evaluate each verse, and what it is saying-

Gen 6:1 And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,

This verse is straightforward. The human population on earth began to increase in numbers.

Gen 6:2 That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.

Now this verse is full of meaning. Some will point to Job 1:6, 2:1 and 38:7 where the same phrase “sons of God” is translated sometimes as angels, and conclude that this also refers to angels as well. The Hebrew words used are – ben: H1121 and ‘elohiym: H430:

1121. ben, bane; from H1129; a son (as a builder of the family name), in the widest sense (of lit. and fig. relationship, including grandson, subject, nation, quality or condition, etc., [like H1, H251, etc.]) …

So the phrase “Sons of God” is a generic term that can mean the subjects or nation of God. It is not a phrase limited to just the angelic host, it has a wider meaning.
The sons of God in Gen 6:2, in context, speaks of those men who were (or claimed to be) obedient to the will of God, they were the people of God, from the lineage of Seth (Gen. 5). In opposition to this are the daughters of men (not obedient to God), from the lineage of Cain (Gen. 4). These woman were quite attractive and alluring, and had little trouble enticing the sons of God into intimate relations and marriage. In doing so, the sons of God quickly abandoned God for these women and their ways.This is basically a retelling of the fall of Adam and Eve. Eve listened to the lies of Satan and doubted God. She ate from the forbidden tree and fell from the spiritual nature she previously enjoyed. That tree was the tree of knowledge of good and evil (Gen 2:9, 17). Upon eating from the tree, Eve was aware of what she had done. She now had the knowledge of evil and she was aware that she had sinned against God. In that knowledge, and having fallen, she then offered the fruit from the tree to Adam.Adam was not deceived (1 Tim 2:14). He knew when he saw Eve that she had sinned, because she had lost the spiritual glow that results from being in close spiritual harmony with God. Moses had this same glow when he came down from Sinai (Exo 34:29, 30). Adam elected to eat the fruit, knowing what he was doing. His love for Eve (whom he knew had sinned) was greater than his love of God.This is a tactic used time and again by Satan. The downfall of God’s people is frequently through the temptations of godless women (See Numbers 25:1-9). Other examples that come to mind are Samson and Delilah, and David and Bathsheba.So, now back to Gen 6:2. The same basic scenario is being repeated after the garden of Eden, only on a larger scale. There is a wholesale abandonment of God and his righteous ways by the descendents of Seth for women of the lineage of Cain, known to be in rebellion and sin. This is what God calls fornication, not referring only to a sexual sin, but the sin of mixing the righteous with the wicked, truth with evil. (One example of this is the word fornication as attributed to the harlot church in Rev 17:4 and 18:3) This sin was so prevalent, and so blatant a rejection of God that it could not be allowed to continue indefinitely.

Gen 6:3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.

God in this verse has just set a period of probation of 120 years on the human race to repent of their wicked ways. It could not be allowed to continue.

Gen 6:4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.

The word “giants” here in the Hebrew is listed in Strong’s as follows-

5303. nephiyl, nef-eel’; or nephil, nef-eel’; from H5307; prop., a feller[*], i.e. a bully or tyrant:–giant.
*Main Entry: ⁴fellFunction: adjective
Etymology: Middle English fel, from Middle French, from Old French — more at FELON
1 a : FIERCE, CRUEL, TERRIBLE b : SINISTER, MALEVOLENT fell

purpose> c : very destructive : DEADLY fell disease>  — Webster’s OnlineSo rather than being perhaps physical giants, in contrast to the meek people of god, these people were rebellious bullies and tyrants, forceful in character and great in their sins. This same phrase of “giants” is also used to describe the Canaanites following the exodus (Num 13:33). Again, this probably referred to their godless and lawless character, as much as their physical stature.

Gen 6:5 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.

The fault here is laid squarely on the wickedness of the people themselves. The first part of this verse is a restatement of the first part of verse 4. As a result of choosing godless women, men were turned away from God as well, and sin and wickedness flourished. God was rejected, and forgotten.

Gen 6:6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
Gen 6:7 And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.

Sin became so great, that God had to bring the flood on them, to cleanse the earth of such great wickedness.

Gen 6:8 But Noah found grace in the eyes of the LORD.
Gen 6:9 These are the generations of Noah: Noah was a just man and perfect in his generations, and Noah walked with God.

Noah was the exception, and he was given the task to build the ark, that would be the refuge from the flood for those obedient to God.
So, now back to the popular story about this passage. Based on a very narrow interpretation of the phrase “sons of God” as found here in Genesis, and bolstered by Job 1:6; 2:1; 38:7; and Psalms 29:1; 82:6, the case is made that this is referring to heavenly beings/angels that interbred with women, causing a ghastly mixed breed of creatures that God had to destroy.

John 1:12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:
Rom 8:14 For as many as are led by the Spirit of God, they are the sons of God.

The above verses make clear that phrase “sons of God” applies to anyone with faith. Note how the righteous 144,000 are described

Rev 14:4 These are they which were not defiled with women; for they are virgins. These are they which follow the Lamb whithersoever he goeth. These were redeemed from among men, being the firstfruits unto God and to the Lamb.

“Not defiled with women” alludes back to Genesis 6 and the sons of God and the daughters of men. The 144,000 walk with God just like Noah, and are not defiled by the great whore of Revelation 17, or her harlot daughters, which are symbolic of apostasy.
So the angelic interbreeding story appears to be nothing more than an attempt to put the blame on angels rather than man. The passage in Genesis 6 speaks only to the wickedness of humanity, and places no blame at all on angels. Humanity had turned their back on God, and did it on such a scale that God was moved to destroy them. Yet, God in His mercy, amid all the wickedness, still did not act hastily to exact his judgment. He gave humanity a period of probation. A time of 120 years, during which Noah could preach the message of God, of repentance and faith. Through that period of probation, people heard the word of God, that they might be saved. Eventually Noah and 7 members of his family were saved in the ark.

Luke 17:26 And as it was in the days of Noe, so shall it be also in the days of the Son of man.
Luke 17:27 They did eat, they drank, they married wives, they were given in marriage, until the day that Noe entered into the ark, and the flood came, and destroyed them all.

It should be clear, to even a casual reader, that we have entered into the days of the Son of Man. History is repeating itself. There are “giants” on the Earth again. The Nephilim, those who follow the way of Cain, and are bold in their rebellion against God, again are filling the earth with sin and violence. Man’s cup of iniquity is again reaching the brim, and God will not let it continue much longer. We have no angels to place blame on, and neither did those people in the time of Noah. Mankind is willfully abandoning God for the sake of the sins of iniquity. Yes, Satan and the other fallen angels can tempt mankind, just as Eve was tempted, but the choice to sin was Eve’s and Adam’s, and is also ours to make. The door of probation is soon to close again on this wicked world, just as it did for the people of Noah’s generation, but this will be for the final time.
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Taken from: http://biblelight.net/nephilim.htm