What does it mean to be set apart for God?

his will clarify as much as possible what does it mean to be set apart for GOD!
I know you heard it many times and i know many times you wondered what exactly can mean something like that! That's why it is very important to have a correct theology and to understand what God is requiring us to do!
People, even those that claim a christian faith have a god that lives only in their very mind.
A god that allows them to live their life as they please and wants them to be happy and them to do whatever makes them happy!
But that god that is like that and does not requires us to be set apart, to be holy is satan.Because not being holy and living just like the godless of this world leads us to no other place but hell itself.
Lets see what it means to be set apart!
Bible verse
Psalm 4:3 You can be sure of this: The LORD set apart the godly for himself. The LORD will answer when I call to him.
. God bless you my beloved friends and see you soon
God bless you all