"Be holy, for I am holy"
"Be not conformed but ..."
"in the world" - "not of the world"
The reality of what holiness means seems to be somewhat vague among Believers, just like godliness. As was explained in the Kingdom Godliness message, their meanings are distinct. (It would be helpful to read that message before reading any further.)
In brief, the difference is this:
Godliness is the disposition of being alive to God (living in the awareness that God is present)
and holiness is living differently (in accordance with the word and character of Christ).
The apostle Peter emphasised the difference when he asked:
"... what manner of persons ought you to be in holy conduct and godliness," 2:3'11.
(Perhaps, the vagueness of understanding is not surprising because of the interrelationship that exists between many of the things of God.)
There is a significant basic distinction between godliness (being alive to God) and holiness (living differently) in that godliness precedes holiness. And godliness produces holiness.
This means that holiness becomes evident when godliness is acted on. However, holy conduct is not produced through a person's own effort.
The Holy Spirit is very much involved because it is He who gives Believers the understandings and the power of these things.