Throughout our prayers we talk about G-d's Kedusha. For example, we say "Ata kadosh", "Nekadesh es shimcha", etc. Kedusha is generally translated as "holiness". Holiness, in turn, generally refers to being "Godly". With that understanding, saying Hashem is Kadosh is circular reasoning - we are saying that G-d is godly, an obvious statement that would not occupy such a prominent role in our prayers.
The Kabbalists, specifically the Ramchal and Nefesh HaChaim, have one understanding of Hashem's Kedusha. I am looking for a non-Kabbalistic approach.
I know that Rashi (Vayikra 19:2 and numerous other places in Chumash) understands Kedusha as seperation. I am not sure what that would mean in reference to G-d.
How would the Rishonim and Pashtanim understand the meaning of Hashem's Kedusha in a way that accounts for its importance?