Though polygamy is deplored by most societies today, its roots are admirable. The Bible stories of Hagar and Ruth illustrate the plight of women in ancient days. It was an extremely hard life. Women did not own property\ and were under the care of their fathers or husbands. So, what happened to widows who have no one to support them? What happened with their children? Where do they go?
Enter the practice of Polygamy.
If the man marries a woman, he has a legal responsibility to care for her. She has a right to receive sustenance and support and an inheritance should he die. Polygamy was the most practical way to care for widowed women and orphans. The woman would be married to the man of the house, so there would be no danger of breaking the Laws of Chastity. The woman would be cared for and, for her part, carry out responsibilities of the household.