During the Middle Ages, women were born solely to marry and to rear children; most importantly, to produce a son for their husbands.
The purpose of this, in a society where women were usually barred from owning property in their own right, was to provide extra resources by which the husband could support his wife, and the children she would presumably soon bear him.
It seems to have been understood that this money was a daughter's share of the family inheritance, and a way for parents to provide for their children's future.
The lord charged a fee, called merchet, when his serfs got married - this was actually a legal test for free or unfree status, since only unfree tenants had to pay.
Families would bargain hard over how large the wife's dowry would be, what prospects for inheritance the husband could offer, and which family would pay the merchet fee.
However, marriage for love was not unknown, and moralists criticised people who got married purely for mercenary reasons.