What is the primary contribution of Christianity as an organized religion to life and culture in the medieval period?

The primary contribution of Christianity to medieval
civilization, may have been, in my opinion, the reestablishment of strong family bonds.
During the Roman empire, the family had become
atomistic.

In Greek times, again in Roman times, and again
in post-classical times, the predominant type of family evolved from trustee to domestic
to atomistic.

The Trustee family
occurred in the earlier stages of civilization, whenever and wherever
neither the state nor the church ruled the family; the family ruled itself. In the
trustee family, the family embraces many households. One man is head of the family but
he is subject to a family counsel and occasionally to the entire family when nearly all
members feel so strongly about an issue that they are willing to oppose
him.

Trustee Family mores include: men
do not openly engage in premarital or extramarital sex. Women do not engage in
premarital or extramarital sex, except for the ever present few blacksliders. Women who
are not virgins cannot marry and are kicked out of the family. Adulteresses also, or
killed if caught in the act.

Property is held in common, is
received from previous generations and is held in trust for future generations. The
family takes care of its own. It is responsible for seeking revenge or compensation for
injury to a family member by an outsider; it is responsible for paying compensation if a
member injures an outsider; costly feuds can
result.

The domestic family
evolves to facilitate commerce. The domestic family is like the
individual household in the trustee family. There is no longer a head of family except
within the household. Property is no longer held in common or in trust, but can be
bought and sold. The family no longer seeks revenge or pays compensation; family members
are now subject to the civil power as regards injuries to or from any other individual.
The family mores remain as in the trustee
family.

The atomistic family
puts individualism above family. Men openly visit prostitutes and keep
mistresses. Fornication is common. Divorce is common, and easy, and marriage is casual.
Children are few or none or neglected. Deviant sexual behavior is common. Abortion is
common. Children do not form strong ties to family, therefore to nothing else either.
People without strong ties are easier to rule, but they do not form a support for the
nation; the nation is easily subjugated by outsiders. Greece was easy prey for Rome when
its family structure became atomistic. Rome was easy prey for the barbarians when its
family structure became atomistic.

After the
fall of Rome, the trustee family structure reappeared in many places,
and the Christian church vigorously promoted the domestic family structure
to replace both the trustee structure and the atomistic
structure.

Zimmerman, Carle C. 1947.
Family and Civilization. New York and London: Harper &
Brothers, 829 + x pages.