Holiness is thus a quality of light. In that sense, we can say that only God is truly holy, because he is pure light

"In a passage from Revelations, St John mentions four living beings surrounding the throne of God. These four living beings, each with six wings and full of eyes, the Christian tradition calls seraphim. Day and night they ceaselessly repeat: 'Holy, holy, holy, the Lord God the Almighty, who was and is and is to come!'. If the seraphim, at the top of the angelic hierarchy, ceaselessly proclaim God's holiness, it is because the word 'holy' best characterizes the essence of the Divinity. But it has been so often used merely to describe men or women who demonstrate a few virtues such as patience, kindness and forgiveness that its true meaning has been lost.

To better understand the meaning of 'holiness', we can turn to the Slavic languages. In Bulgarian, for example, the words svet, 'holy', and svetost, 'holiness', have the same root as the word for light, svetlina. Holiness is thus a quality of light. In that sense, we can say that only God is truly holy, because he is pure light. This is what the seraphim repeat, and it is why holiness is also inscribed in their name, which in Hebrew is Hayoth haKodesh, 'animals of holiness' (where 'animals' is obviously taken to mean 'living beings')."