In one of his last letters to Wilberforce, John Wesley wrote in 1791:

Dear Sir,

Unless the divine power has raised you to be as Athanasius contra Mundum, I see not how you can go through your glorious enterprise in opposing the inexcreble villainy which is the scandal of religion, of England and of human nature. Unless God has raised you up for this very thing, you will be worn out by the opposition of men and the devils. But if God be for you, who can be against you? Are all of them together stronger than God? O, be not weary of well doing! Go on, in the name of God and in the power of his might, till even American slavery (the vilest that ever saw the sun) shall vanish away before it.

...

That He who has guided you from youth up may continue to strengthen you in this and all things, is the prayer of, dear sir,

Your affectionate servant, John Wesley

Q. In this letter what is the meaning and significance of the phrase 'Athanasius contra Mundum' in the context of his (and Wilberforces) anti-slavery crusade?