'Duty' in the Bible

“When a man takes a new wife, he shall not go out with the army nor be charged with any duty; he shall be free at home one year and shall give happiness to his wife whom he has taken.

“When brothers live together and one of them dies and has no son, the wife of the deceased shall not be married outside the family to a strange man. Her husband’s brother shall go in to her and take her to himself as wife and perform the duty of a husband’s brother to her.

But if the man does not desire to take his brother’s wife, then his brother’s wife shall go up to the gate to the elders and say, ‘My husband’s brother refuses to establish a name for his brother in Israel; he is not willing to perform the duty of a husband’s brother to me.’