Throughout the Bible, spiritual growth is depicted as a gradual process. Here in Philippians, Paul is speaking of those who, because of their spiritual immaturity, do not have an overwhelming desire to know Christ. Many think that we should not be fanatical about our faith, but this is not borne out in the Bible. The Bible encourages, even requires, such fanaticism. Yes, Paul could try to yell, scream and argue the younger Christians into maturity, but this would not be effective.
Prayer is more effective than argument.
Leave such work up to God. There are few better examples. Of course, Paul was only a worthy example insofar as he followed our supreme example, that is, Christ. Throughout the Bible, we are not only given commandments concerning how to live our lives, but also examples of saints living godly lives. Examples are a very powerful method of instruction, giving life to the commandment.