Genesis 4  Cain is the firstborn of Adam and Eve.  This is after the fall and the curse of painful childbirth.  Perhaps this is why Eve proclaims "I have gotten a man child with the help of the Lord ".

Cain was "tiller of the ground".  This was his love.  He desired this above anything else, even above God.  He chose to bring an offering to the Lord from his fields.  Something he did with the sweat of his brow and his own hands.  This is not acceptable to the Lord. Cain becomes angry that the Lord does not respect this gift.  His anger leads to jealousy, which leads to murder.  The result for Cain is judgement.  He is cursed with the loss of his ability to cultivate the ground.  He becomes "a vagrant and a wanderer". Then " Cain went out from the presence of the Lord".  He starts his own city.  He becomes the father of a clan.  They do great things - Jabal institutes tent-dwelling and livestock, Jubal institutes the arts, "the lyre and pipe"; Tubal-cain is a forger of implements of bronze and iron, tools.
But it never says that they worshiped God again.
Cain had a choice and his wrong, sinful choice led to a society of godless people. One person's choice affects more than just himself.  God warned Cain, and He warns us. " If you do well, will not your countenance be lifted up? And if you do not do well, sin is crouching at the door; and its desire is for you, but you must master it." (v7)  Cain's "countenance fell" because of his anger.  He lost control of his conduct and his attitude.  He let sin in the door.  He let it devour him instead of mastering it.  He only had to confess and repent. To choose God's way over his own.  But he refused.  Even after he killed his brother, he never repented.  He just complained about the punishment.

Abel is the second born son.  He is a keeper of sheep.  He brought an offering that God respected, a firstling of his flock. He worshipped properly. This brought about his brother's jealousy. He is murdered by his brother Cain. And his blood cried out to God. Hebrews 11:4 speaks of Abel, " By faith Abel offered to God a better sacrifice than Cain, through which he obtained the testimony that he was righteous, God testifying about his gifts, and through faith though he is dead, he still speaks."
And in Hebrews 12:24 Abel's blood is compared with the blood of the new covenant, the blood of Jesus which "speaks better than the blood of Abel."

Chapter 4 ends with the birth of Seth.  Abel is dead, Cain is an outcast, but God gives Adam and Eve another son. It is from his line that we have Noah, Abraham, David, and finally Jesus. Eve considered Seth a replacement for Abel, appointed to her, from God. Gen. 5:3 "When Adam had lived one hundred and thirty years, he became the father of a son in his own likeness, according to his image, and named him Seth."   Seth carries on the likeness, the family resemblance of his father Adam.
This begins a long line of descendants who carry on this image. And it is in this generation that "men began to call upon the name of the Lord."

Chapter 5 gives the lineage of Adam, made in the image of God,  through until the life of Noah. 10 generations.  All having many sons and daughters.  All living hundreds of years.  Massive reproduction!  Unique among the many are Enoch, who walked with God so closely that God took him, and Noah.  Noah's father, Lamech, made an interesting statement about his son, "This one shall give us rest from our work and from the toil of our hands arising from the ground which the Lord has cursed." There was something special about Noah right from the beginning of his life.

Father, thank You for Your Word that reveals all Truth.  Thank You for helping us to see what the life of faith looks like and what the life of sin leads to.  Help us to always choose to live for You, in obedience to Your Word, in relationship with You.  Help us to walk with You like Enoch did.  We call upon Your Name, the only Name by which we can be saved.  Help us to abide in You and know that You abide in us.  Through Jesus, the True Vine.  Amen.