As made clear by the play's epigraph, the phrase A Man for All Seasons is meant to apply to More himself. Robert Whittonton, a writer from More's time, used the phrase to say that More was the kind of guy you would want at your back in any situation.
A court case? You want More. A philosophical discussion? You want More again. A rollicking good time? You just need more More, baby.
More's unquestionable greatness only highlights the tragedy of the play. After all, if the best, most intelligent, and most morally good man in the world ends up with his head on a pike, then what hope do the rest of us have going for us? Sadly, it's this grim question that keeps ringing in our ears after reading through the entirety of A Man for All Seasons.