Gwang gives an extensive account of Wesley's move to ordain ministers, especially for America. He shows how Wesley derived his understanding of ministerial orders -- particularly as it pertains to the differences between presbyters and bishops -- from the Puritan-influenced (but still very Anglican) King's and Stillingfleet's historical work.
What it came down to at the time was an argument from necessity. There was no other way to accomplish the end in view within the canons of the Church of England, so Wesley stepped outside them to do what (in his view) he had the innate ability to do. Up to that time, he had, as a dutiful son of the Church, scrupulously obeyed every rule regarding orders and the sacraments. but in order to provide for his followers in America, he went beyond the rules. Assuming for the sake of argument that the theory he derived from King and Stillingfleet held good, his actions would be seen (borrowing RC lingo) as "valid but not licit."
Gwang doesn't use such language, of course. Coming as he does from Korea, there is a lot of Calvinist Protestantism bred in his bones. He's as Methodist as they come, to be sure, but he frequently betrays a tendency to emphasize Word over Sacrament, and to occasionally assume the basic rightness of historic Protestant assertions about Catholic theology (without bothering to prove his assumptions).
But the nub for me, is that he never really addresses the core of the Necessity argument. For neccesity doesn't just mean that every proper desire must have some way of fulfillment, so if you are blocked at every turn you may properly step outside the box you find yourself in and do as you will. That is the Scotch view of the state of nature: "I am among barbarians who refuse to do justice, therefore, the social contract is null and void and I am returned to a state of nature and am justified in doing justice as and how I think meet."
No, given what I have read by Wesley about his own reflections on the Methodist movement -- which surprised him very much and succeeded against even its leader's inclinations and prejudices -- I am convinced that Wesley believed that the blessing of the Spirit of God on the Methodist movement had been objectively demonstrated. In other words, it was the will of God that Methodism survive, as it was the (ever-surprising) will of God that John Wesley should lead it. He had been called, and given responsibility, and he felt he could not simply shrug and say, "Well, I tried."
This is a very different kettle of fish from, "I've got to find some way to accomplish this goal." It was, to Wesley, a matter of choosing to obey God rather than men.
In the end, of course, neither Catholic nor Covenanter will accept Wesley on these terms. It is of no matter to me that they don't. I'm just saying that if you want to understand Wesley -- as Gwang Seok Oh wants to, and mostly does -- then you have to understand the weight of the necessity argument he used to justify his actions. For Wesley, it was a command from God -- rather like the dominical expression, "you give them something to eat," I think. He acknowledged that the bishops he approached for help were perfectly free to refuse to help him, and he didn't blame them; but that did not absolve him of the direct responsibility from God to take care for the souls God had placed within his extraordinary cure.