" When we recognize that there are unbelievers in the visible church, there is a danger that we may become overly suspicious. We may begin to doubt the salvation of many true believers and thereby bring great confusion into the church. Calvin warned against this danger by saying that we must make a “charitable judgment” whereby we recognize as members of the church all who “by confession of faith, by example of life, and by partaking of the sacraments, profess the same God and Christ with us.”9 We should not try to exclude people from the fellowship of the church until they by public sin bring discipline upon themselves. On the other hand, of course, the church should not tolerate in its membership “public unbelievers” who by profession or life clearly proclaim themselves to be outside the true church. "
― Wayne Grudem , Systematic Theology: An Introduction to Biblical Doctrine