Again, I like Pink on this. Please, take time to note the reasons and cause for this and the connection to Gen 3:15 & Rev 12.
[emphasis mine]
"We turn now to consider the occasion of the Flood. "And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them, 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. 6:1, 2). There has been considerable difference of opinion among commentators and expositors in respect to the identity of these "sons of God." The view which has been most widely promulgated and accepted is, that these marriages between the sons of God and the daughters of men refer to unions between believers and unbelievers. It is supposed that the "sons of God" were the descendants of Seth, while the "daughters of men" are regarded as the offspring of Cain, and that these two lines gradually amalgamated, until the line of distinction between God’s people and the world was obliterated. It is further supposed that the Deluge was a visitation of God’s judgment, resulting from His peoples’ failure to maintain their place of separation. But, it seems to us, there are a number of insuperable objections to this interpretation.
If the above theory were true, then, it would follow that at the time this amalgamation took place God’s people were limited to the male sex, for the "sons of God" were the ones who "married" the "daughters of men." Again; if the popular theory were true, if these "sons of God" were believers, then they perished at the Flood, but 2 Peter 2:5 states otherwise—"Bringing in the flood upon the world of the ungodly." Once more; there is no hint in the Divine record (so far as we can discover) that God had yet given any specific command forbidding His people to marry unbelievers. In view of this silence it seems exceedingly strange that this sin should have been visited with such a fearful judgment.
In all ages there have been many of God’s people who have united with worldlings, who have been "unequally yoked together," yet no calamity in anywise comparable with the Deluge has followed. Finally; one wonders why the union of believers with unbelievers should result in "giants"—"there were giants in the earth in those days" (Gen. 6:4).
If, then, the words "sons of God" do not signify the saints of that age, to whom do they refer? In Job 1:6, Job 2:1, Job 38:7, the same expression is found, and in these passages the reference is clearly to angels. It is a significant fact that some versions of the Septuagint contain the word "angels" in Genesis 6:2, 4. That the "sons of God," who are here represented as cohabiting with the daughters of men were angels—fallen angels—seems to be taught in Jude 6: "And the angels which kept not their principality but left their own habitation, He hath reserved in everlasting chains under darkness, unto the judgment of the great day."
These "sons of God," then, appear to be angels who left their own habitation, came down to earth, and cohabited with the daughters of men. Before we consider the outcome of this illicit intercourse, let us first enquire into the cause of it. Why did these angels thus "sin" (2 Pet. 2:4)? The answer to this question leads us into a mysterious subject which we cannot now treat at length: the
"why" finds its answer in Satan.
Immediately after that old serpent, the Devil, had brought about the downfall of our first parents, God passed sentence on the "serpent" and declared that the woman’s "Seed" should "bruise his head" (Gen. 3:15). Hence, in due course,
Satan sought to frustrate this purpose of God. His first effort was an endeavor to prevent his Bruiser entering this world. This effort is plainly to be seen in his attempts to destroy the channel through which the Lord Jesus was to come.
First, God revealed the fact that the Coming One was to be of human kind, the woman’s Seed, hence, as we shall seek to show,
Satan attempted to destroy the human race. Next, God made known to Abraham that the Coming One was to be a descendant of his (Gen. 12:3; Galatians 3:18; Matthew 1:1); hence, four hundred years later, when the descendants of Abraham became numerous
in Egypt Satan sought to destroy the Abrahamic stock, by moving Pharaoh to seek the destruction of all the male children (Ex. 1:15, 16). Later, God made known the fact that the Coming One was to be of the offspring of David (2 Samuel 7:12, 13); hence,
the subsequent attack made upon David through Absalom (2 Samuel 15). As, then, the Coming One was to be of the seed of David, He must spring from the tribe of Judah, and hence
the significance of the divided Kingdom, and the attacks of the Ten Tribes upon the Tribe of Judah!
The reference in Jude 6 to the angels leaving their own habitation, appears to point to and correspond with these "sons of God" (angels) coming in unto the daughters of men. Apparently, by this means,
Satan hoped to destroy the human race (the channel through which the woman’s Seed was to come) by producing a race of monstrosities. How nearly he succeeded is evident from the fact, that with the exception of one family, "all flesh had corrupted his way upon the earth" (Gen. 6:12). That monstrosities were produced as the result of this unnatural union between the "sons of God" (angels) and the daughters of men, is evident from the words of Genesis 6:4: "There were giants in the earth in those days." The Hebrew word for "giants" here is nephilim, which means fallen ones, from "naphal" to fall. The term "men of renoun" in Genesis 6:4 probably finds its historical equivalent in the "heroes" of Grecian mythology. Satan’s special object in seeking to prevent the advent of the woman’s "Seed" by destroying the human race was evidently an attempt to avert his threatened doom!
Against the view that "the sons of God" refer to fallen angels Matthew 22:30 is often cited. But when the contents of this verse are closely studied it will be found there is, really, nothing in it which conflicts with what we have said above. Had our Lord said, "in the resurrection they neither marry, nor are given in marriage, but are as the angels of God" and stopped there, the objection would have real force. But the Lord did not stop there. He added a qualifying clause about the angels: He said "as the angels of God in heaven." The last two words make all the difference. The angels in heaven neither marry nor are they given in marriage. But the angels referred to in Genesis 6 as the "sons of God" were no longer in heaven: as Jude 6 expressly informs us "they left their own principality." They fell from their celestial position and came down to earth, entering into unlawful alliance with the daughters of men. This, we are assured, is the reason why Christ modified and qualified His assertion in Matthew 22:30. The angels of God in heaven do not marry, but those who left their own principality did.
Ere we close, there is one other passage of Scripture which ought to be considered in this connection, namely, Matthew 24:37 —"But as the days of Noah were, so shall also the coming of the Son of Man be." History is to repeat itself. Ere the Lord returns to this earth, the condition which prevailed in the world before the Flood are to be reproduced. The characteristic of the days of Noah may be summarized in the following ten items: 1. Multiplication of mankind (Gen. 6:1)—note the great increase of earth’s population during the past century. 2. God dealing in long-suffering with a wicked world. 3. God sending His messengers to warn sinners of coming judgment. 4. God’s Spirit striving with men, and the threat that He would not always do so—(cf. 2 Thess. 2), which tells of His Spirit being taken away once more. 5. God’s overtures toward men despised and rejected—such is the condition of the world today. 6. A small remnant who find grace in the sight of the Lord and walk with Him. 7. Enoch miraculously translated—typifying the removal of the saints from the earth caught up to meet the Lord in the air. 8. Descent to the earth of the fallen angels and their union with the daughters of men: how near we have already approached to a repetition of this may be discovered in the demoniacal activities among Spiritists, Theosophists and Christian Scientists. 9. God’s judgments poured forth on the ungodly—of Revelation 6 to 19. 10. Noah and his family miraculously preserved—type of the Jewish remnant preserved through the Tribulation, see Revelation 12."
http://www.pbministries.org/books/pink/Gleanings_Genesis/genesis_11.htm
