In Ancient times marriages were promoted and conducted by the fathers of the bride and the groom. It was a very serious ceremony.
The main goal of the marriage was to have children, since bringing more children into the world was of considered to be a matter of utmost importance.
The second goal was to promote the economic and political situation of the two fathers, by connecting unrelated families or strengthening the bond between those already related.
This was done by exchanging daughters between families. One family member's daughter would marry the other family member's son. She would then leave her family home and move to live with her new family. In return, the family receiving the daughter as a bride would then send their own daughter to marry the in-laws' son and live with them. In this way, larger family connections would be formed.
The exchange of one bride for another ensured that the bride would have the highest status in her new family. She would be considered the Senior Wife, at least at the start of the marriage.
Another variable that would decide the seniority of the wife would be that of her fertility status and if she would provide her husband with male offspring.
If a family did not have a daughter to offer in exchange for a bride, then they were required to give a Mohar.
A Mohar, or dowry, was a compensation given by the groom or the groom's father when they did not have a daughter to offer.
We see an example of the use of a Mohar in the Bible in the instance of Isaac and Rebekah. Abraham did not have a daughter to offer in exchange for Rebekah, so as a form of compensation, he gave presents, silver, and gold.
"...Then the servant brought out jewelry of silver, jewelry of gold, and clothing and gave to Rebekah. He also gave precious things to her brother and to her mother"
(Genesis 24:53)
Another example is found in 1 Samuel, when King Saul offers his daughter Michal to David, causing David to panic at the proposal.
"...Does it seem to you a light thing to be a King's son in law, seeing I am a poor and lightly esteemed man?..." (1 Samuel 18:23)
"Then Saul said, "Thus you shall say to David: 'The King foes not desire any dowry but one hundred foreskins of the Philistines...'" (1 Samuel 18:25)
It was always preferable to give a daughter in exchange for a daughter, rather than to give a Mohar. This way, you could be a bit more sure that the daughter you had given would be treated more fairly.
Furthermore, any children born to the bride and groom would be considered the children of the groom's family and not of the bride's family. Thus, if a family did not receive a bride in exchange for their daughter, then this would deny them the opportunity to also receive children.
Children were power in Ancient times. They could work to help build and advance the family, to provide for them, protect them, and give the family a strong future.
Jacob's Mohar
Jacob's Mohar was for him to work seven years for Laban in order to receive Rachel's hand in marriage.
Laban had arranged a feast for Jacob, and over the course of the feast, Jacob found himself somewhat inebriated from the alcohol he had consumed.
Laban, who had an interest and priority to wed his older daughter Leah (who had "delicate eyes", probably due to a disability), sent Leah to Jacob's room to lay with him.
Jacob, unable to distinguish between Leah and her sister Rachel, complied, and after the act, was obligated to wed Leah.
Leah, with her disability (her delicate eyes), should have been offered for free as a concubine.
Jacob was considered to be a refugee and had received refuge and protection from Laban. Such was his inferior status (as a refugee) that he could not demand to avenge his honor. Laban exploited Jabob's situation and said that it was not acceptable for him to wed the younger sister before the older.
In a normal situation, Jacob could demand satisfaction and worthy compensation for his work Mohar, but his status was not normal, since he was a refugee.
Eventually, Jacob paid twice for Rachel's Mohar. The first was when he married Leah (giving her the status of Senior Wife), and the second was when he eventually married Rachel.