Love not the world is pretty simple to understand. Why Bob’s conscience will allow him to do things that are a sin for Lucy is difficult to grasp.
Holiness preaching is not some advanced subject for grad students.
Babies need to know as part of their foundational knowledge that God is holy and requires us to be holy.
That starts in our character and behavior, and will ultimately find its way to our outward appearance.
2 Peter 1:5-9
5 And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;
6 And to knowledge temperance; and to temperance patience; and to patience godliness;
7 And to godliness brotherly kindness; and to brotherly kindness charity.
8 For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.
9 But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins.
Notice that faith, which is the foundation, is followed by virtue—moral excellence in the Greek.
This is where holiness begins.
It’s milk.
Charity, which is the final quality mentioned, is where we learn to be gracious and exercise Christian liberty.
That’s meat.