Its been said that “if there is no God then all things are permitted.”
Well, that’s why we have laws. Precisely because all things are permitted. Murder, adultery, theft, war, etc. All of these things happen and are able to happen and are thus permitted.
Laws are created to curb that permission.
If there is no law then all things are permitted.
Hopefully the above sheds light on the meaning of the quote. The quote is an appeal to moral authority and a sense of how things ought to be. Many things are not permitted in the world as it ought to be but all things are permitted in the world that lacks an appeal to morality (an appeal to how things ought to be).