Genesis 4-5. Three chapters into God's story the Priest-King and his bride have been kicked out of Eden. Excluded from the presence of God. Cursed. And yet shown grace and given promises. There will be a seed. And then they have sons. Cain and Abel. Both these priests offer worship. One is accepted the other isn't. Abel offers worship in faith (Hebrews 11v4), which must be in response to the word of God (Romans 10v17). Cain however is idolatrous in worship. Cain is of the evil one (1 John 3v12) - a seed of the serpent. Is he then not responsible for his action? No, he is accountable. Sin crouches at his door and as human being he should rule over sin. He's made to reign in life. And yet he succombs to it. Sin rules him. And he kills his brother. The darkness of Genesis 3 is darker still.
Confronted by the LORD who still relates to his excluded priests Cain denies responsibility for his brother, the one he has killed. But, the LORD hears the blood of Abel speak. It speaks curse from the ground onto Cain. One day there will be a seed of the woman, murdered by a seed of the serpent, whose blood will not just speak curse but curse-averted. For now this murdered man's blood speaks of curse. He is Hebel (meaningless - Ecclesiastes 1 etc) and all hope seems to be lost. The serpent's seed is striking the woman's seed, and is seemingly victorious.This line was promised and it's coming is heart-breaking and defames the LORD.
Graciously the LORD protects Cain under the weight of curse as he faces the second exile (our 'first parents' to use Calvin's term were exiled from the garden, now he is exiled again). If anyone kills Cain the LORD declares a seven-fold vengeance. Vengeance is the LORD's, even for Abel's murder. Cain's family go and then settle. They build a city instead of scattering over the whole earth, and presumably it is like the next city (11v4) where men gather to make a name for themselves rather than filling the world - though city will come to be a term of great redemption in the new creation (Revelation 21-22). Cain's line comes to Lamech. This brute marries two women and rules as a tyrant. Where is forefather Cain denied murder, aware of it's wrong Lamech glories in murder. And then usurps the LORD again by declaring vengeance not seven but seventy-seven times (contrast Peter's query about forgiving seven times, Jesus would say seventy-seven). This serpent's seed is horrendous. And these are the people multiplying. Things are bleak.
But, then we rewind. Another seed of the woman - Seth! And in his day human beings begin to call upon the name of the LORD. From this line come a truer people. Outstanding among them Enoch and another Lamech. Enoch walks with the LORD and then is not. Unlike all the rest he does not die but proceeds to be with God - returned to Eden? A great hope! We know him to be a prophet (Jude 14) declaring that God will come in judgement. It will happen, when? Surely soon. Sin will not go unpunished though Lamech of Cain revels in it. Then just as Seth was a son, and named so too is Noah of Lamech. This SON will bring relief from curse. Judgement is coming as Enoch prophesied but there is hope of relief. What a sweet sound! What a moment. How? When? We wait to find out. But there is hope. Though the serpent has been striking the woman's seed God's promise holds true. Next: Genesis 6-8.