Mike O:
To deviate a bit from the first question, is not incest a grave mortal sin? Even at this time when incest was perhaps “necessary,” how can the mortal nature of a sin be dispensed with merely over time?
Not “merely over time”, but in specific situtations. Look into Israel’s laws concerning this.
It is true incest was normally strictly forbidden:
Leviticus 18:16 Thou shalt not uncover the nakedness of thy brother’s wife: because it is the nakedness of thy brother.
Leviticus 20:21 He that marrieth his brother’s wife, doth an unlawful thing, he hath uncovered his brother’s nakedness: they shall be without children.
However, a “dutiful” incest was also practised among the tribes of Israel for posterity, and those who did not were subject to severe punishment:
Deuteronomy 25:5
When brethren dwell together, and one of them dieth without children, the wife of the deceased shall not marry to another: but his brother shall take her, and raise up seed for his brother: 6 And the first son he shall have of her he shall call by his name, that his name be not abolished out of Israel. 7
But if he will not take his brother’s wife, who by law belongeth to him, the woman shall go to the gate of the city, and call upon the ancients, and say: My husband’s brother refuseth to raise up his brother’s name in Israel: and will not take me to wife. 8 And they shall cause him to be sent for forthwith, and shall ask him. If he answer: I will not take her to wife: 9 The woman shall come to him before the ancients, and shall take off his shoe from his foot, and spit in his face, and say: So shall it be done to the man that will not build up his brother’s house: 10 And his name shall be called in Israel, the house of the unshod.
Genesis 38:8 Juda, therefore said to Onan his son:
Go in to thy brother’s wife and marry her, that thou mayst raise seed to thy brother. 9 He knowing that the children should not be his, when he went in to his brother’s wife, spilled his seed upon the ground,
lest children should be born in his brother’s name. 10 And therefore the Lord slew him, because he did a detestable thing.
So if it was to ensure tribal posterity, then how much more so human posterity at the time of Adam and Eve (and likewise immediately after the flood).
By the way, this law prohibiting incest came 430 years after the time of Abraham. Abraham himself was married to his step-sister (Gen 20:12). Tobias also married his uncle’s daughter. (Tob 8:9).
hurst