n lieu of physical trips, the college-focused evangelism and discipleship organization is working to organize “virtual mission trips,” including virtual prayer walks using Google Maps and sharing the gospel with students at international universities through social media. Though optimistic about the push for online evangelism (one Cru website has recorded up to 2,300 decisions for Christ per day), Higgins acknowledges that volunteers on the ground are “really critical” for Cru’s work.

The story is similar at other mission organizations. Approximately 20 percent of all US-based international mission work each year is done by short-term volunteers, according to an analysis by sociologist of ...