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.
Master the “milk”…or backslide
This episode expands on the theme that Christians at a certain point should be able to teach the basics to others. If they're not, then they are on the equivalent of spiritual "welfare." Consumption of "milk" without putting the Word into practice characterizes their Christian experience, and spiritual growth is put on hold indefinitely, as they are "dull in hearing." All Christians are expected to grown in maturity into the stage of young men and women who, according to 1 John 2:12-14, have victory over the enemy because they put into practice the Word of God which abides in them. Serving the living God rests on knowledge of the Word of God and mastery of "milk," the foundational principles of the Christian faith (Hebrews 6:1-2)