MORE: Why not be a teacher? You’d be a fine teacher. Perhaps even a great one.

RICH: And if I was who would know it?

MORE: You, your pupils, your friends, God. Not a bad public, that.

Robert Bolt (1924-1995) English dramatist

A Man for All Seasons, play, Act 1 (1960)
    (Source)

More trying to convince Rich not to seek a public or political office (because of the corrupting influences he would face).

Rendered almost identically into the 1966 film adaptation.

MORE: Why not be a teacher? You’d be a fine teacher, perhaps a great one.
RICH: And if I was who would know it?
MORE: You. Your pupils. Your friends. God. Not a bad public, that.