Sexual intercourse between persons too closely related for normal marriage. The twofold theological rationale for the prohibition of incestuous unions is the divine claim “I am the Lord your God” (Lev 18:2,4,6) and the note that such behavior characterized the Egyptians and
Canaanites whom God judged (Lev 18:3, 24-25). Leviticus 18:6-16 prohibited unions between a man and his mother, stepmother, sister, half sisters, daughter-in-law, granddaughter, aunt (by blood or marriage), or sister-in-law. Leviticus 18:17 prohibited a man’s involvement with a woman and her daughter or granddaughter. Leviticus 18:18 prohibited taking sisters as rival wives. Penalties for various forms of incest included childlessness (Lev 18:29; 20:17-18; cp 1 Cor 5:2,5), and death (Lev 20:11-12,14). in patriarchal times marriage to a half-sister (Gen 20:12) and marriage to rival sisters (Gen 20:12) and marriage to rival sisters (Gen 29:21-30) were permissible, though such marriages proved troublesome to both Abraham and Jacob. Scriptural accounts of incest include (Gen 19:31-35; 35:22; and 2 Sam 13).