'Duty' in the Bible
"When a man is newly married, he must not be sent out to war or have a related duty placed on him. Let him stay home for one year and be happy with his wife whom he has married.
"When two brothers are living together and one of them dies without leaving a son, his widow must not be married outside the family to a foreigner. Instead, the brother-in-law must go to her, take her as his wife, and by doing so perform the duty of a brother-in-law.
But if the man does not want to marry his brother's widow, then she must go to the elders at the city gate and declare, "My husband's brother refuses to perform the duty of a brother-in-law in order to preserve the name of his brother in Israel. He is not willing to perform the duty of a brother-in-law.'