A reader in the comments of the last post suggests, reasonably enough, that the link between church attendance and number of friends might be due to extraversion.
The MIDUS Study has measures of Big 5 personality traits, but the closest I can find for friends is the extent to which one gets support from friends. Here are the OLS regression results:
OLS Regression Coefficients (standardized, sample size = 3,885)
Church attendance .09
Negative emotionality -.06
Openness to experience .04
All relationships are statistically significantly, and all except negative emotionality are associated with more support from friends. Even after we adjust for Big 5 traits, attendance predicts more support. It is the strongest predictor after extraversion and agreeableness.