One could easily imagine statistically that for any large group of people who upon reflection would not call themselves followers of Christ, there would be some people more interested in talking about spiritual things than others. And it seems reasonable that if possible spending your time in conversations with people who are more interested than others would be more productive and useful than with those who are positively inclined against it or indifferent.
If that’s true then the question becomes how do we identify the more interested from the less interested and spend our time with the former?
Of course we can exercise good timing at asking questions and discovering teachable 
moments. There are a number of ways to do that in a diplomatic and non-manipulative way, but that’s not what we want to discuss here.
Portrait of Young Man With a Red Cap
Sandro Botticelli: Denver Museum of Art
Photo: JAC
A very good way of “locating” people who are possibly or probably in teachable moments about the gospel, is to create what we call filtering experiences. We call them that because people who attend or get involved in some way self-select for interest in the gospel and spiritual things. One effective way to do that is by holding events where people are invited (not coerced) to attend activities that are clearly “advertised” as having to do with spiritual things. For example, holding a debate on the existence of God, or a colloquium where a speaker is speaking on issues that clearly identify herself as a Christian or speaking from a Christian point of view could provide a “filtered” experience. That is, if the invited person come to the meeting with her “eyes wide open” about the content then in some sense she has “passed” through a filter that an uninterested person might not.
This does not mean they had a positive response to what the speaker or the event had to say about the gospel, but it does show some interest.
But say at those meetings there were response cards or reaction cards or some sort of follow-up cards where people who attended the event are asked to describe their response, give their name, address, and contact information, and who write a positive response. Then another “filter” has been passed through if they fill one of those out. And I think you can see that as people pass through more and more of these “filters” you could begin to assess the most interested people in the things of the gospel.
As a Christian community matures you can see the value of their creating many, many events that give people an on-going opportunity to express their interest in the gospel and with proper forethought create filters for those experiences. The value of on-going events is that it can accommodate the fact that people’s interest in the things of the gospel often wax and wane and are hard to predict. So setting up an attractive, positive and engaging “institution” like this can create a situation where people are spending their time with the most interested people.