In the context of enumerating the advantages of addressing believers as "saints" without reference to "church," this episode brings home the evidence of professed sainthood: works and growth in Christ. The episode cites the parable of the dragnet (Mt 13:47-50), which claims that many "bad fish" would associate themselves with the visible church, without actually being saints. And Christ said as much in Matthew 7:22-23, where association with Christ without conversion would be commonplace among nominal believers at the judgment. One of the common features that Scripture cites as evidence of saving faith is works. While believers are not saved by works, the natural manifestation of saving faith is subsequent good works. He who abides in Christ naturally bears fruit. (John 15:5) Those who merely associate with Christ in the visible church "practice lawlessness." (Mt 7:23) Peter held that Christians should grow spiritually. Failure to progress minimally indicates "blindness" or "short-sightedness" and MIGHT indicate that one has not received the calling as a saint. Peter admonishes believers "to make certain about his calling and choosing." The Biblical expectation of sainthood is therefore demonstrable fruit and works.
Your Calling and the Local Church
This episode is a realistic primer on encountering opposition when doing ministry. The presumption so far has been that most opposition comes from unbelievers outside of the church. But Christ's own description of the visible church indicates that both wheat and tare would congregate together. Together with carnal believers, ministers of the gospel should expect opposition and resistance from both groups, who naturally voice their opinions based on the degree of carnality in which they operate. All the lessons of Nehemiah still apply: whether doing ministry in the church or outside, Christians are called to remain focused on executing their tasks based on God's vision for their lives, not dwelling on the discouraging comments of the unspiritual.