Genesis 4 is unique because it contains one of the only descriptions of the pre-flood world. Man was cursed and cast out of the garden— Genesis 4 is the first glimpse of life outside that paradise.
It quickly becomes evident that man did not learn from the first sin in the garden. Man's nature had become corrupt— and it didn't take long for man to demonstrate his wickedness.
Hypocrisy brewed. Cain sought to deceive God with a half-hearted offering. His anger grew and he murdered Abel, his own brother. But God, by His grace, was merciful. He gave Cain the opportunity to repent, but Cain refused.
After the murder, the first family was divided— Cain left his home for the land of Nod. He constructed the first mentioned city in Scripture and named it after his son Enoch. Enoch became the father of Irad, who became the father of Mehujael, who became the father of Methushael, who became the father of Lamech.
Lamech entered into a polygamous relationship with Adah and Zillah. Through these two wives, Lamech became the father of three famous sons. All of them are noted for their various accomplishments, but none of them are mentioned for being righteous men who sought after God. Jabal was the father of those who dwell in tents and have livestock, Jubal was the father of those who play the lyre and the pipe, and Tubal-cain was the forger of all implements of bronze and iron.
Genesis 4 also contains the second recorded death in human history. In two short verses, Lamech explains to his wives that he killed a man for striking (and wounding) him. Once Lamech is finished giving his short explanation of the killing, the account of Cain's descendants is brought to an abrupt end.
Eve gives birth to another son— Seth, the second man in Christ's lineage. Thus Genesis 4 ends with a glimmer of hope. In the midst of all the pain— in the midst of all the death and immorality— in the midst of all of this, Genesis 4 closes with the following statement: Then men began to call upon the name of the LORD. (Genesis 4:26)
Summary of Genesis 5
Outline of Genesis 4
Summary of Genesis 6