The Marriage and Religion Research Institute has published a list of 162 Reasons to Marry. The reasons, obviously, are too many to list, but here are a few:

The findings herein demonstrate that in marriage are contained all the five basic institutions, all the basic tasks, of society: family, church, school, marketplace and government. These fundamental tasks, well done, in unity between father and mother, make for a very good marriage. Within a family built on such a marriage, the child gradually learns to value and perform these five fundamental tasks of every competent adult and of every functional society. Gradually he is mentored in them, often unconsciously. Gradually she learns that she is expected to act similarly. Eventually, he and she become more and more expert in performing all five tasks. In other words, they gradually grow in competence and are ready to strike out into society and, eventually, to build their own family. How they do that will depend much on what they experienced in growing up in their families of origin.

Spousal Relationships
1. Married couples enjoy more relationship quality and happiness than cohabiters.[10]
2. Those who marry experience increased commitment and stability.[11]
3. Men raised in married families have more open, affectionate, and cooperative relationships with the women to whom they are attracted than do those from divorced families.[12]
4. Married mothers report more love and intimacy in their romantic/spousal relationships than cohabiting or single mothers.[13]

Poverty
1. The married family is less likely to be poor than any other family structure.[71]
2. Marriage between the biological single parents of impoverished children would move 70 percent of them immediately above the poverty line.[72]
3. Marriage decreases a child's chances of living in a low-income condition.[73]
4. Marriage among the poor nearly doubles their probability of moving from a poor neighborhood to a non-poor neighborhood.[74]
5. Children from married families are less likely to experience poverty than children from any other family structure.[75]
6. The children of married mothers experience more upward economic mobility than children of divorced mothers.[76]
7. Married couples are less likely to receive welfare.[77]
8. Five percent of children from married families receive public assistance, compared to 25 percent of children from cohabiting families.[78]
9. Intact married families are less likely to have participated in the Food Stamp Program (now SNAP, the Supplemental Nutrition Assistance Program).[79]