A Chrestian is somebody struggling to be righteous and good in all their actions (from the Greek word Chrestus - a Good or Useful person).
A Chrestian may have a Pagan religion in which case they accept that the Chrestian Path is not necessarily the right path for everybody all the time. Alternatively a Chrestian may have an Exclusive Chrestian religion (such as mainstream Zoroastrianism) which does teach that people should follow the Chrestian path exclusively.
Chrestianism is particularly important where social conditions cause people to be interacting with each other who do not have strong natural ties with each other. Chrestianism encourages people to do the right thing to help others regardless of the other's status.
Chrestianism can be practiced opportunistically and in a direct way with the people one happens to meet in which case the most important quality needed is an attitude of benevolence towards others. Chrestians may also act more holistically in seeking to improve the world order. In this case they are trying to change things remote from their immediate experience and they need not just benevolence but also great wisdom to ensure that their good intentions are directed to the best effect.