Genesis 4 - 6

Ok, so by chapter 3, Adam and Eve had gone past the stop sign and gone directly to jail. They were cast out of paradise and entered the world of toil and struggle, in which we still live. In chapter 4, we have the first-ever murder, even a fratricide, when Cain kills his brother, Abel. Seems a bit of jealousy was created when God accepted the offering of Abel's animal, but rejected Cain's offering of fruits and vegetables. We assume both boys were instructed in the proper offerings to God by their earthly father, Adam. God's sacrifice of an animal to cover Adam and Eve after they sinned set the pattern for the kind of offering God accepts. So, we have to conclude that Cain's offering was in disobedience to God. God lectures Cain about it, and warned him about having a bad attitude, but that attitude prevailed longer, as Cain lured his brother out into the field where he killed him.
Here we find that God sees everything. Although Cain thought he was being sly by taking Abel into the woods where the deed was hidden, God knew what he had done. So Cain compounded his sin by lying when God questioned him as to Abel's where-abouts. He gives what has become a universal statement of non-responsibility when he responds with, "Am I my brother's keeper?" God cursed Cain, but showed mercy in that He allowed him to live longer, however, as a marked man. Cain was driven away from his family to become a nomad.
Then, we get the question of Cain's wife. Where did Cain get his wife? Well it could have been a sister or niece. Cain was probably a grown man when he killed Abel. Adam and Eve, no doubt, had other children in the meantime. Or God could have made a wife for Cain as simply as He made Eve. That's not a stretch if one believes in an omnipotent God.
Adam and Eve then had Seth, from whose lineage Jesus will come many years in the future. Chapter 5 mainly traces that lineage from Seth down to Noah, who would be only one of four men to survive a worldwide flood. Also in chapter 5, we find a strange reference to a man named Enoch in the lineage of Seth, who was a worshiper of God and who did not experience death. He simply disappeared from the earth. "Enoch walked with God; then he was not, for God took him."--Genesis 5:24. Elijah, an Old Testament period prophet, is another who was taken in a like manner. In Revelation, we see the return of two prophets, who will testify to Israel in end times. I wonder if these two men will be Enoch and Elijah, who are being kept in their human forms awaiting their return to earth to fill these roles.
By chapter 6, God is fed up with man's sinfulness. He is ready to destroy us all and start over. There is a strange reference to Nephilim in Verse 4, that has led to much speculation. Some believe the Nephilim were fallen angels who were intermarrying with humans. Nephilim simply means giants, so I rather think it was a large race of people who resulted from all the close marriages within families that was taking place. Humanity was already very depraved and forgetful of God.
Except for Noah. Noah still worshiped God, so God decided to let him live. In His great mercy, he also gave Noah plenty of time to preach to his neighbors to try to save some while he was building the ark that God instructed him to build. Until that time, there had been no rain on the earth. There was just a cycle of dew at night to water the plants and sunshine during the day, so the people probably thought Noah was crazy. They didn't know what rain was, let alone a flood, so they disregarded him and his preaching and only Noah and his immediate family were saved from the flood.
Questions abound as to how Noah would have gathered up all those animals and gotten them into the ark, but again, if you believe God can do all things, why could He have not caused the animals to simply come to the ark and enter it? I believe He could have. The scripture seems to bear this out, as we read in Chapter 7, verses 8 and 9, "Pairs of clean and unclean animals, of birds and of all creatures that move along the ground, male and female, came to Noah and entered the ark..." and again verse 15 repeats the same thing as reinforcement, but I've gotten carried away and gone into tomorrow's chapter.