John Donne presents subtle thoughts expounded through wit that is often of the ironic kind. Using Donne's "The Undertaking" as an example, he uses irony and witty comparisons to expound the thought that men ought to, in fact, see and love women's virtue (Stanza 5) while he overtly makes the opposite point, "And a braver [thing] thence will spring, / Which is, to keep that hid."
Donne sets the mood of his subtle ironically presented thought by saying that men who love the color connected with women (e.g., skin, eyes, rosy cheeks, bright garments) metaphorically love only "their oldest clothes." This is a witty turn of phrase and concept to speak of the shallowness of superficial love. He prepares for the twist in his message that comes in the ending by pointing out that the valuation and love he spoke of in Stanza 5 receives derision from "profane men."
Donne gives the turn of the screw in the last stanza when he says that therefore men are right to keep their high opinion of women's virtue hidden, which is to ironically say that those who do so are hypocrites, cowards and knaves. The witty comparison that starts the poem in Stanza 2 compares gemstones to women and men who see and value the virtue of women as gem cutters who have newly learned their art but who are unable to practice it. This comparison ties in with his final tongue-in-cheek admonition to keep opinions valuing women's virtue hidden. This ironic, witty construction would have a much readier reception than a didactic admonition to value women rightly.