In a nutshell, holiness is the separateness of God. It just means distinct and different. At least that is how I explain it.
There are some who say it is a foundational attribute of God. Maybe. But, I have a question.
What is it about God that makes Him holy?
Imagine someone who lived in a cave, separate from all things that would cause you to do anything wrong. That would, in a way, be holiness. Some monks of some religious orders do this. But that isn't what God's holiness is like.
Now, picture someone who lived among people, with all the temptations and problems that go along with it, and still being kind to them. Even when they don't deserve it! That is what makes God holy.
Anyone can be kind and loving to those who do it to them first. But God, does it to everyone. Good and bad. Big and small. He cares about and wishes the best for everyone. It's a tough concept for me to wrap my mind around.
He wants everyone to be with Him. He wants what is best for everyone, and He wants it all the time. Unfortunately, some of us, don't want it from Him. And oddly, He never forces us to accept kindness and love. But, that is another topic.
I could ramble around in a circle, but I am just trying to say that God is holy because He loves. He doesn't love us because He is holy. He is holy, simply because He loves us.
Find a way to be kind and encouraging to someone today.
Especially someone you don't like.
Watch what happens.
On the other hand, you could point out others failings and faults.
Imagine continually doing that to everyone.
Would you be liked?
Think about it.