Christianity is important to our society because it serves as a moral rudder.
Morality is necessary for a society to exist.
Some standards must exist for people to follow or society will decay and eventually collapse, as did the Roman Empire. The focus of morality, on the other hand, is to avoid behavior proscribed by political and religious authorities. The ethical teaching is lost in the effort to enforce a religious code or standard. Generally, from the standpoint of ethics, Christianity has been a dismal failure. Centuries of religious intolerance, warfare, and persecution have proven this beyond any reasonable doubt.