The Bible never defines holiness as such, especially when applied to God; rather, it is a term which in many respects signifies the otherness of God, the Godness of God if you will - how he is so utterly and wholly unlike us in his divine attributes. It speaks of the uniqueness of his being.  It is a term often associated with the radiance of God (Shekinah) which far outshines anything we could imagine. It is sometimes linked to ‘glory’, the weight of God (kabod), which outweighs the entire cosmos. The absolute, transcendent, otherness of God - his holiness - is conveyed in the vision of chapter 4 in several ways.