He associates 'holiness' with purity, priesthood, and proclamation. In the next few days we will look at each of these. Lord, I choose to be holy. Now teach me what that means. Holiness is associated in Peter's words with a couple of things, one of which is purity.
Purity simply means being 'uncontaminated' in a polluted world, an impure environment.
This is the real meaning of holiness, too. This idea of 'separateness' is implied even in non-Christian uses of the word 'holy'. This shrine established in the hearts of men as on the solid earth it commemorates a people's fortitude and sacrifice. So help me, Lord, to be separate, holy. For your glory.