Hendricks frames this as a formula: growth ∝ (member contacts × attractiveness × ease of joining). Each variable matters, but the first one — member contacts with non-members — is the gating factor.
A church with excellent programming and zero member relationships with unchurched people will not grow. There’s no channel through which anyone new arrives.
A church with mediocre programming and members who maintain genuine friendships with unchurched people will grow, because the channel is open and working.
This has a name in network theory: open vs. closed networks. Open networks expand through weak ties — acquaintances, neighbors, coworkers — not through close relationships. The weak ties are the growth edges. As churches grow inward and deepen existing bonds (which is good), the weak ties with outside people thin and eventually disappear.
The practical measurement: for each member, how many genuine ongoing relationships do they have with people who aren’t in the church? If most members can’t name any, the growth surface is near zero.
This doesn’t require grand outreach programs. It requires members who have jobs, hobbies, neighborhoods, and families that include unchurched people — and who remain genuinely engaged in those relationships rather than retreating into church community exclusively.