Genesis 9: 20 – 22: And Noah began to be an husbandman, and he planted a vineyard: And he drank of the wine, and was drunken; and he was uncovered within his tent. And Ham, the father of Canaan, saw the nakedness of his father, and told his two brethren without.
After the Fall, there were two lineages of humanity living side by side on the earth. These were the children of God, descended from Adam through Seth, and those of the Serpent, descended from Cain. With the passage of time, the spiritual state of the righteous line waned whilst the evil traits of the Serpent’s seed multiplied and strengthened until they overwhelmed the others. According to Genesis 6: 1 – 2, the sons of God (the descendants of Adam) took to wife the daughters of men (the female descendants of Cain). The sons of God had become attracted to the daughters of men because of their beauty and married them. In the course of time, this intermarriage swallowed up the righteous lineage and humanity became one flesh and one blood.
Because of the union between the godly and the ungodly seeds, only one righteous man remained on the earth according to Genesis 7: 1: And the LORD said unto Noah, Come thou and all thy house into the ark; for thee have I seen righteous before me in this generation. This means that Noah’s sons were hybrid because his wife was not of the Sethite lineage, and the wives of Noah’s sons were not of the pure righteous seed either, so the seed of the Serpent crossed into the new world with Noah through Noah’s wife, his hybrid sons, and their wives. The Flood wiped out the pure Serpent’s seed and the pure sons of God (with the exception of Noah). Humans existing on the earth today are a cross between the two lineages.
The sin of Ham in seeing his father’s nakedness is understood by looking at the Book of Leviticus. Leviticus 18: 8: The nakedness of thy father’s wife shalt thou not uncover: it is thy father’s nakedness. Leviticus 20: 11: And the man that lieth with his father’s wife hath uncovered his father’s nakedness: both of them shall surely be put to death; their blood shall be upon them. To have sexual relations with one’s father’s wife was equivalent to uncovering or seeing the father’s nudity. This is what Ham had done. Noah had only one wife, and she was Ham’s mother. Ham’s sin was incest with his own mother. Whether Ham’s mother was drunk like Noah was, or a willing participant, the scripture does not tell us.
Just as the fall of Man in the Garden of Eden was caused by sexual perversion, the fall of the new race that was to replenish the earth after the Flood began in the same way. Adam was commissioned to multiply and replenish the earth, but he and his wife fell through sexual sin. Noah and his family were similarly commissioned to multiply and replenish the new earth, but they too fell by the same ruinous sin.