Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills. And he who associates others with Allah has certainly fabricated a tremendous sin.
Meaning:-
“Allah does not forgive association”: means that God does not forgive shirk—the sin of worshipping or attributing divine powers to anyone or anything besides God—if a person dies without repenting from it
Fabricated: false, and invented or produced in order to deceive someone