Hearts Refreshed in Christ

Philemon deals with a real-life example of Christian fellowship being worked out in the relationship between a Christian slave owner (Philemon) and his runaway but now converted slave (Onesimus). Paul commends Philemon as one who "refreshed the hearts of the saints in Christ" and he asks him to do this again in his behalf.
What does this phrase mean? How can we refresh others in Christ and receive refreshment from them?