I have some questions about the sentence below.
Why is there a comma before "that"?
Next, if we say "But of all relations" the verb of this sentence should be plural. So, why is there "was sure" in the sentence instead of "were sure"?
But of all relations, that between men and women, being the nearest and most intimate, and connected with the greatest number of strong emotions, was sure to be the last to throw off the old rule, and receive the new; for, in proportion to the strength of a feeling is the tenacity with which it clings to the forms and circumstances with which it has even accidentally become associated. . . .
(The Enfranchisement of Women, Harriet Taylor Mill)