(Gen. 6:2) describes before the account of the flood “that the sons of God saw the daughters of men, that they were beautiful,. and they took wives for themselves of all whom they chose.” Who are the sons of God? and who are the daughters of men?
The sons of God are the descendants of Seth and the daughters of men are the descendants of Cain.
After the slaying of Abel the righteous, Adam begot another son and named him Seth, “for God has appointed another seed for me instead of Abel” (Gen. 4:25) “And as for Seth, to him also a son was born; and he named him Enosh. Then men began to call on the name of the LORD.” (Gen. 4:26). In the genealogy of Jesus Christ it is mentioned that “the son of Enosh, the son of Seth, the son of Adam, the son of God.” (Luke 3:38).
The sons of Seth were called the sons of God for they were the sanctified offspring from which Noah came, then Abraham, then David, then Christ through whom all the tribes of the earth were blessed. They are the believers that belong to God; those took the blessing of Adam (Gen. 1:28) and then the blessing of Noah (Gen. 9:1).
It was good that God called some humans His sons before the flood.
The sons of Cain were not attributed to God for the curse that befell Cain, befell them also (Gen. 4:11) and they walked in the way of corruption so they were called the sons of men and they all drowned by the flood.