6 Controversial Bible Passages the Skeptics Love to Hate—Explained
3. A widow must marry her brother-in-law? (Deuteronomy 25:10)
This is a passage that teaches "levirate marriage" (which was quite common in the ancient world). "Levirate" comes from the Latin word levir, meaning "brother-in-law." The law states that if a man has a wife, but he dies without an heir, she must marry his brother so that they can have a child to inherit the man's possessions. Sounds terrible to our modern ears, doesn't it?
But in the ancient agrarian world, it was practical and merciful. If a widow did not have any children from her first husband, then the land could be sold off, and she would be left destitute. By marrying her brother-in-law, she would be keeping the property (which she may have brought into the family) within the family. She and her family could lose the property if she married someone from the outside. The brother-in-law could refuse to marry her, but according to verses 7-10 she could go through a ceremony to publicly shame him into marrying her.
In marriage the woman would be financially secure and she would have children to take care of her in her old age. Sounds strange to us today, I know, but that was the "Social Security/Medicare" set-up of the ancient world.