Ps 1. gives the principles of spiritual separation from the world. As was pointed out by others: It is not a bunch of do's and don'ts, separation is a life style, a mode of being (of existing), a condition of the heart. To be seperate unto God is also to be holy (the term defined).
It is God who has made us holy unto Himself, not by our works or effort. Our job is to live as though we actually believed that our oliness is an established fact. But, as no two vessels are exactly alike, neither are the requirements as to their individual use. To take a vessel used for old wine and force it to hold new wine is begging for discord and “rebellion”, and to scapegoat the vessel for the failure of the wine master will not work. The owner of the vineyard is neither blind nor easily fooled. The wine master shall indeed be held accountable for his misuse of the owners resources and the loss of both the new and old wine.
Another way of putting it is: We are to judge things with a righteous judgment, as God judges, not as man judges. But, as long as we are in the mode of comparing ourselves to one another and establishing levels of holiness (separation from the world) according to our own standards of righteousness, we shall continue to fall short of the glory of God. [This is another subject/thread.]
Ask any parent who has a “large family”, say three or more kids. If you treat all of them in exactly the same way, requiring exactly the same standards of dress, talents/abilities, behavior, interest, language, etc. you will end up killing off your kids – or they, you. Do not expect all to want to become hockey players or violinist. To like red dresses or only blue. One boy may want to shave his head(short hair means to be shaven in some eyes), the other to let his hair cover his ears. In many of such cases we would play Solomon; and to resolve the issue of the hair length would be to either cut of the boys ears (remove the standard), or their heads (remove the source of contention). This is the approach so many have taken to these kinds of issues, i.e., we strive for uniformity over unity, and wonder what there is so much strife and discontent within the church body.
We have way too many would be masters within the church body and not enough devoted servants.