Dating someone with the express purpose of converting the other person to a given religion (usually Christian) rather than building a sincere relationship with them. Very often, the "missionary" will dump the person they are dating once they believe that person has been "saved". This is a very bad idea because it insults the potential convert and the faith of the person attempting the conversion. Not only that, it can damage any future relationships for one or both.
Guys and gals, if you're out there "dating for Jesus" or whatever your equivalent might be, you're causing more harm than good. On top of that, you're using the same tactics as the Moonies and Reverend Jim Jones (look up "Jonestown Massacre"). So quit it, you idiots.
Content that she'd won Bob over to Christ, Sara publicly dumped him at the local coffee shop. Bob had trouble trusting women or the church for years after that and Sara's dating prospects dried up once word got out about what she was doing. Yep, "missionary dating" sure did wonders there.