It's a two-step process, when you think of it.
The first step is to distort certain bible passages, in particular the one pertaining to the 'faithful slave', in order to convince members, and potential converts, that there is only one true religion, one organization that god is using.
Once this has been accomplished, they move on to phase two: convincing members and potential converts that they are that 'faithful slave' that god is using. They accomplish this by process of elimination, by exposing the false teachings, or what they perceive as such, of all other religions. In other words, every other religion is wrong, therefore, theirs must be right.
It is not by the merits of their own religion, or the words and actions of their leaders that JWs are convinced they have the truth. It by the falsehoods and misdeeds of all others. Proving yourself true isn't important, proving others false is.