And you shouldn't marry any woman whom your father has already married except what happened previously, indeed it is a shameful, odious, and evil way.
In the ignorant period when the father died, his widow wife was married by the son; and if the son dies, his widow was married by the father. Also, the widows were considered as an asset for inheritance. Lord is teaching that all such deeds are shameful, odious, and against nature. By the revelation of this verse, all such marital relations were stopped forever. The child born through such relations before revealing this verse shouldn't be considered as bustards. Lord has explained through Messenger that anyone who is making sexual intercourse with a woman with whom marriage is prohibited, should be killed.
Today, since there is no group of believers anywhere in the world, these laws can’t be implemented. In this Last era, the odd believer should live by holding fast Adhikr with his molar teeth. The bachelor and spinster believers should accept the virgin Maryam (the mother of Jesus) as the role model, whereas the married believers should accept Asia (the woman of Pharaoh) as the role model. The believer should follow a mode of prayer and lifestyle as explained in verses 7: 205-206. See explanation 2: 2-5 and 23: 7.