The Bible is candid regarding its perspective of mankind. Since the Bible is the Word of God, this shows that God is fairly transparent in regards to the way He sees mankind and the way He feels about the decisions His creation makes. The assessment that God provides is seldom favorable about human beings, which shows that people have historically been unable to please God and proven to be as unrighteous as the Bible declares.
In Genesis 6:1-4 the Bible talks about the decisions that people were making as they began to populate the world. The world was not old. The ink of God's signature of His creation had not yet dried (figuratively speaking). Nevertheless, only 6 chapters into the Bible's contents and two murders had been committed, three curses had be issued, and Genesis 6:1-4 shows mankind compounding the problems that were already created. The testimony of Genesis 6:1-4 shows what happens when a group of people stops seeking God, and starts making decisions for self.
In Genesis 6:1-4 the Bible describes a group called "the sons of God." Bible scholars and students have been puzzled about the use and meaning of this phrase for a long time. This phrase is difficult to translate because it is used in two different ways throughout the scriptures. In the Book of Job, the phrase "sons of God" is used to refer to fallen angels that sided with Satan in his rebellion. The apostle Peter in his writings to describe the same demonic angels uses this same phrase. However, the phrase "sons of God" is also used in the Book of Deuteronomy to refer to children of the line of Seth. Therefore, the phrase could also be used to refer to people in the line of Seth who married into the cursed line of Cain.
Genesis 6:1-4 also introduces the word "Nephilim" into scripture. Many people are intrigued about the identity of the "Nephilim." The word "Nephilim" comes from the Greek word "gigantes," which is where the English word for "giants" comes from. There are some who have interpreted Genesis 6:1-4 in such a way that they assume the Nephilim to be a sort of "super race" of human beings, even to the extent of gods, thereby introducing polytheistic theories. This is untrue. The text makes the identity of the Nephilim quite clear. Though the scriptures do describe them as large men, the scriptures are clear to identify them as men. Though the Nephilim may have been the result of relationship between demonic spirits and worldly women, the affect was human - not godlike.
The point of Genesis 6:1-4 is not to focus on who the Nephilim are. God's purpose in Genesis 6:1-4 is to illustrate the corruption of mankind. The scriptures show that the sons of God saw the daughters of men and found them beautiful. Consequently the scriptures describe the sons of God "taking for themselves wives." There are a few problems with this description. First, one must recall that when Adam was joined with Eve, it was the work of God that made such happen. Marriage is the work of the Living God, and scripture is clear to show that He is the One who brings people together in marriage. Yet Genesis 6:1-4 shows the sons of God responding to the desires of their flesh, making their own decisions without regards to God, and chaos is the result. In that the scriptures show the sons of God "taking" wives, it is an illustration that these men were taking women by force. Then, one must pay attention to the plurality of the phrase "wives," showing that these men were taking many women for themselves. Genesis 6:1-4 describes an environment motivated by fleshly lusts, violent relationships and rebellion against God. Whether or not the sons of God are fallen angels almost becomes irrelevant. Either way, the people on earth are acting in demonic ways as they live contrary to the will of God.
The scriptures then go on to explain the perspective of God regarding this lustful and wicked behavior. Genesis 6:1-4 documents God saying that "His Spirit" would not strive with mankind forever because "they are flesh." God will not "strive" with mankind. This means that God will not contend with people. He is God. He doesn't have to deal with the wickedness and foolishness of human decisions. He chooses to patiently deal with His creation, but He will not be mocked and contend with mankind as if we are His equals. The reason God says this is because He presents a contrast that shows that people are not like God, though much of human decision-making and reasoning reflects the belief that we can be like Him. The scriptures shows that God is Spirit, but mankind is mere flesh. Though the Bible says that we were made in the image of God, we are not like Him. He is greater. He is superior. He is sovereign. He is the Living God that transcends and controls all things by His eternally almighty power and infinite wisdom. The contrast between the concept of "Spirit" and "flesh" would be equal to a contrast between black and white, or light and dark in Biblical context.
Thus, God decreed judgment upon the sons of God and all the people of the earth. Since God looked at the people on earth, and found that they ignored Him, rejected Him, and sought to live without Him, God would not "strive" with people and force Himself upon them. Nevertheless, there is consequence for living without God. Though God is just to decree judgment, His patience and mercy is revealed in the manner that His judgment was decreed. Though God had the right to destroy mankind in the Garden, at the death of Abel, and in the midst of the corrupt fleshly relationships that mankind had desired, God gave the world 120 years to live as a chance to repent. God provided 120 years of time to accomplish two things: to give mankind adequate time to repent, and to show that when judgment came, His justice was right because adequate time to repent was given. With 120 years to repent, God would not be at fault for judgment. 120 years worth of time places reasonable accountability on people to hear the voice of God, repent from sin, seek God, and as Enoch was, walk with God.
Nevertheless, Genesis 6:1-4 states that the world was famous for its corruption. The Nephilim became well-known because of their stature and their conduct. The world began to embrace the violent and lustful temperament of the Nephilim, so that instead of rejecting such living, the world accepted such conduct as "good" and turned from the righteousness of the Living God. God's judgment was just and deserved. In the New Testament, Jesus compared the days before His 2nd Coming to the days described in Genesis 6:1-4, which means that just before His return, the world will resemble the environment of Genesis 6:1-4. If one is honest with one's assessment of the world today, one will find a concerning amount of similarities. If God judged then, and was righteous at that time, He will judge again as promised, and will be right for doing so again. Yet, just as in Genesis 6:1-4, He is patient and merciful to grant adequate time for repentance in order to receive salvation from His wrath, showing that God does not change.