God's declaration in Genesis 6:5 reveals that humans in Noah's time were entirely evil, from their innermost intentions to their outward actions, leading to the divine judgment of the Flood. Despite this catastrophic event, God states in Genesis 8:21 that the imagination of man's heart remains evil from his youth, indicating that the Flood did not alter human nature. He acknowledges a brief window of potential goodness in early childhood, yet asserts that due to their flesh, humans are inclined toward selfishness and sin. This corrupt nature persists in humanity after the Flood and throughout history, showing no improvement in moral character. Scripture consistently illustrates the depth of human sinfulness, as seen in David's words in Psalm 14:1-3, Isaiah's descriptions, and Jeremiah 17:9, which labels the heart as deceitful and incurably wicked. Paul, in Romans 3:9-18, indicts all of humanity, noting that while not all are flagrant sinners, even a single sin incurs the penalty of death in God's eyes, highlighting the pervasive corruption that begins from a young age.

God declares His assessment of humanity's moral state just before the Noachian Flood, stating that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually. This stark depiction in Genesis 6:5 contrasts sharply with God's earlier evaluation in Genesis 1:31, where He saw everything He had made as very good. In a relatively short span, humanity degenerated from unspoiled to rotten to the core, illustrating a total depravity that resulted from losing contact with the God of creation. God meticulously observed and scrutinized mankind's behavior over an extended period, watching their steady moral deterioration from purity to wickedness since the expulsion of our first parents from the Garden of Eden. This decline was not a short-term event but a continuous corrosion over centuries until the Flood. God describes this wickedness as great, indicating not just naughtiness but true evil, corruption, and immorality that multiplied exponentially across the earth. This universal condition of sin was pervasive, affecting every region with no area spared from the destruction it brought. Further intensifying this judgment, God notes that every intent of the thoughts of man's heart was only evil continually, emphasizing an internal corruption that drove external violence. Their attitudes sparked wicked thoughts and plans, producing more evil in everything they did. Their hearts contained only evil, with no good remaining, and this evil was ceaseless, constant, and perpetual, dominating their thoughts and deeds from morning until night. This comprehensive depiction underscores a state of total depravity in humanity before the Flood.

Reformed Protestants, often called Calvinists, teach a Doctrine of Total Depravity, which posits that all humanity is sinful, possessing no goodness that can satisfy God. This teaching suggests that while human nature is not completely depraved, it is totally affected by depravity, so that sin taints even the good that people do. Since Adam and Eve ate of the Tree of the Knowledge of Good and Evil, humans have been a mixture of good and evil, but like wine injected with poison, the good in people is corrupted by evil. Even acts of human love and altruism are ultimately driven by selfishness, ego, pride, covetousness, or some other sinful motive. Human nature is indeed marked by corruption and evil, with all having sinned and fallen short of the glory of God. Men and women are sinful and in need of a Savior.