Why did John Knox reject the offer of the bishopric of Rochester?
In a lecture on the historical background to the Westminster Standards, around minutes 12–13, Sinclair Ferguson mentions that John Knox was offered the bishopric of Rochester, "whether to give him more scope for ministry or to silence him." Per Wikipedia, the offer was given because Knox was seen as a "useful political tool."
Knox turned down the offer, but it's not clear to me what his motivation was. Did he see it as an attempt to silence him or co-opt his ministry, or for some other reason? Did he explain why in any surviving documents? If not, is there a consensus among historians?