"In the unfallen world, nakedness was a symbol of integrity and sinlessness ( Genesis 2:25), but in the fallen world, it became a sign of exploitation, captivity, abuse, and shame ( Leviticus 3:7; Leviticus 3:11)." [1][source]
Note the parallels between this legislation and the story of Ham looking on his father Noah"s nakedness ( Genesis 9:20-27). Both acts resulted in a curse ( Leviticus 18:24-28; Genesis 9:24-27). Both acts also connect with drinking wine ( Leviticus 10:9; Genesis 9:21). God was guarding His people from falling into the same type of sin and its consequences that Ham experienced. One writer suggested that God designed the legislation in chapters18-20 to guard the Israelites from what humankind did at Babel ( Genesis 11:1-9). [2][source]
God prohibited intercourse with married or unmarried individuals outside marriage. In Israel, engaged couples were considered as good as married, though they had not yet consummated their marriage with intercourse. Moses mentioned twelve different situations in these verses. [source][source][source]
"Marriage as a social institution is regarded throughout Scripture as the cornerstone of all other structures, and hence its purity and integrity must be protected at all times." [3][source]
"After the death of her husband a woman may not marry her brother-in-law [4]. Deuteronomy 25:5 ff. states an exception to this principle. Should a woman be widowed before she has borne a Song of Solomon , her brother-in-law has a duty to marry her "to perpetuate his brother"s name" ( Leviticus 18:7). This custom of Levirate, attested elsewhere in Scripture and the ancient Orient, illustrates the paramount importance of having children in ancient times. Heirs prevented the alienation of family property and ensured the parents" support in their old age, in times when pensions and other welfare services were unknown." [5][source]
Translators have made a fairly strong case from philological, literary, and historical considerations for translating Leviticus 18:18 as follows. "And you shall not take a woman as a rival wife to another...." The Qumran community translated it this way. If this translation is correct, the verse explicitly prohibits polygamy and implicitly prohibits divorce. [6]):199-214; Gleason L. Archer Jeremiah , A Survey of Old Testament Introduction, p259; and Walter C. Kaiser Jeremiah , Toward Old Testament Ethics, p189. John Murray also preferred this interpretation in Appendix B of Principles of Conduct, pp250-56.] Thus the Mosaic Law forbade some things that the patriarchs practiced: marrying one"s sister ( Leviticus 18:11; cf. Genesis 20:12) and marrying two sisters ( Leviticus 18:18; cf. Genesis 29:30). [source][source][source]
"What has troubled biblical scholars for some time are the two major omissions from the list: father-daughter incest and brother-sister incest. Economic reasons might have made these two violations rare in the ancient Israelite world. A virgin daughter brought a good bride-price. If a father violated her, he lost that. A corrupt father more likely turned his attentions elsewhere than to his daughter. This might also apply to a brother, as seen in the case of Laban, the brother of Rebekah, who actually became the head of the family and negotiator for marriage in the place of his father." [7][source]