Gen 6:4 indicates in the Bible that the Nephilim existed in the earth during those days and in the same days it was happening that the sons of God went to the daughters of man and fathered them offspring. They were the heroes of bygone, men of fame. The question that has been raised by many is who were these giants and why have they been mentioned in the Bible. In my knowledge, the giants, or Nephilim, were peculiar creatures and inhabited the earth prior to the great flood during the era of Noah.
Other scholars are of the opinion that the sons of God in this verse were angels who descended to earth. They also got married to human women and their children were very powerful and renowned. These youngsters were known as Nephilim that translates to giants. They were not merely tall and strong but they were also reputed to be powerful and influential to people. I believe this demonstrates that the world before the flood was quite different than the one nowadays. Human beings were not that innocent and sin was increasing among humans.
The giants were known as heroes of old due to their odd nature of being powerful, brave and skillful. According to some bible teachers, their existence in the earth made more evil and this made God sad. According to Genesis 6:5, the Lord looked and saw how corrupt the race of men had become on earth and all the tendencies of the thoughts of the human heart could do, were nothing but evil. I believe this is an indication that the giants were among the factors that made God resolve to bring the flood in order to purify the earth.
Although the giants were strong, they were not eternal. The fact that God decided to send the flood was a lesson to us that as much as a person may be powerful, God is more powerful. I also learn something in life here, that being great to the world does not necessarily imply that one is good in the sight of God. The Nephilim could have been mighty and renowned, however, they belonged to a sinful world.
Finally, the giants in Gen 6:4 were very special creatures who came about as a result of the inter-marriage between angels and humans. They were powerful and well known yet their presence revealed the extent of the spread of sin on earth. Reading their stories helps me to understand that the wisdom and the justice of God is above human power or popularity and I should live in a manner that brings Him joy.