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Boswell took notes on Johnson's talk soon after it happened and rebuilt it later as dialogue, with the speakers named. This made the subject's character show through his exact words and his quick replies rather than through the biographer's summary. The reader judges the man directly from what he said, the way a witness would.
Boswell argues that small habits, odd gestures, off-hand remarks and domestic trivia show who a person is more truly than public achievements do. He includes Johnson's tics, his eating habits and his fears on purpose, because these unguarded particulars let the reader see the whole man rather than a monument.
Boswell arranged for Johnson to dine with John Wilkes, a radical Johnson despised, by getting him to commit to the dinner before he learned who else was coming. The episode shows that personal antagonism often fades in direct company when people find common ground and pride keeps them from walking out.
Boswell puts himself in the story openly. He provokes Johnson with questions, sets up situations and records his own embarrassments, so that the subject shows himself by reacting. Seen this way, the biographer's relationship with the subject is not a flaw to hide. It is the tool that draws out material which could never be recovered from documents alone.