When you consider the period of time from fall to flood, you may want to consider whether or not you read it in the context of a Dispensational (Dispy) or Covenantal (Covs) framework. If you grew up in certain churches, one of these frameworks may have already and unknowingly been impressed upon you.
Dispys emphasize a discontinuity, in that, from fall to flood is a separate age or dispensation of God’s management of mankind. Cain, Lamech, Seth, Noah and the rest are ruled/governed by God, who entrusts them to follow their own consciousness, as having the law written upon their hearts. The test is inferred from the NT (Rom. 2:12-15, 5:22-14) but is not directly mentioned in the immediate Genesis content (a problem for the hermeneutic of strict progressive revelation). There is also the Dispy notion that all dispensations end in a judgement, but they fail to discuss why the judgement upon Cain and other such judgements do not constitute additional dispensations.
Post-fall, the newest guidance from God can be summarized as the promise of a Redeemer/Messiah. The rest is either continuity (be fruitful and multiply) or the resulting consequences of the fall (expulsion from the garden, work the ground for food, pain in childbearing…).
To say this age is separate from the others, because mankind had their conscience to guide them, is not persuasive. Man has his consciousness in all ages, and so it is always man’s burden to bear. This is not unique to this age. To insinuate that man had no other guidance from God negates the normal believer experience whereby it is said that they called upon the LORD (Gen. 4:26). To the claim that because of the fall God spoke less often, is negated by God speaking directly to Adam after the fall, to Cain at both his offering and later at his excommunication, Enoch was said to walk with God (inference of communication), and speaking extensively with Noah. There is no quantitative way to conclude that God changed in His dealing with man, except for the new need for salvation. Man is still and always required to love God with all his heart, soul, strength, and mind.
Covs teach that the continuity is the greater context, so no division is made of tests of God’s management. The law is written on man’s heart in all ages (not just this one), Man is to have faith in God in all ages, and as pointed out in prior posts, the language of covenant relationship dominates the immediate text.
With these points in mind, Covs read this age in a relational/covenant context. Post-fall we see how the first visible family (or church) handled God’s promise. Adam’s family, although in possession of the gospel, becomes a mixed multitude (as like Israel and/or the church) There is the wayward lineage of Cain, culminating in the twisted view of Lamech who boasts of murder and believes God will protect/avenge him. The other lineage of Seth seems quite godly in nature. Seth’s children call upon God, Enoch walked with God, and it culminated in Noah, who found grace in God’s eyes.
Reading these progressively we get to where Noah’s father, a different Lamech, likely thinking of the promises, offers a prediction that Noah will bring relief from the toils of hard labor/farming. But we encounter a problem. The two lines of Seth and Cain have merged back together, as the sons of God take and marry the daughters of man (Gen. 6:2). I know the alien, fallen angel, and demonic possession theories, but they are just fantasies created when the texts are pulled apart and not viewed covenantally. Covenantally and systematically we see this recurring problem that the visible believers/people of God, who appear to be following God outwardly, still fall into sin. Israel will do the same thing again and again as they inter-marry with pagan people in Canaan, having been forbidden to do so. Solomon, Sampson and others will have the same issue with wives, and throughout Judges the people fall back into sin quite habitually. This merger plunges mankind into such a depth of sin that God determines to start over (in rough terms) with Noah. Thus God is keeping his promise to provide a Messiah (one He will provide himself) and yet is just to exercise eternal and temporal judgements upon the earth and its inhabitants. Post-flood we will see much of the same continuity.
This covenant context keeps the reader focused on God as promise maker and keeper, although working through sinful people to bring about fulfillment. Mankind is blessed to have the promise of salvation by grace through faith (of those whom God chooses), but struggles to work this out in everyday life in perfect gratitude. Without this, the text is likely read, and usually presented to children, as moralistic lessons. Again, this type of separating the law of God from his character, will result in both tendencies to legalistic and antinomian beliefs.