In Sonnet 4, beauty is a loan and the handsome bachelor a bad banker
Shakespeare's fourth sonnet talks about good looks the way an accountant talks about capital. Nature does not give beauty away, it lends it, and a young man who spends his only on himself is a miser, a failed moneylender and, at death, an estate with nothing to show the auditors.
Almost every line borrows from the vocabulary of money and inheritance. The addressee is hailed as unthrifty loveliness and later as a beauteous niggard, a phrase that fuses admiration and scolding. His beauty is a legacy, a bequest, a largess and a sum of sums, all words that imply it was meant to pass through his hands to someone else rather than stop with him.
The central idea is that Nature lends rather than donates, and lends most freely to the generous. Hoarding that loan is therefore a kind of fraud. The speaker calls the young man a profitless usurer, a striking insult in an age suspicious of lending at interest: he handles an enormous fortune yet somehow cannot make it earn a living. Trading only with himself, he ends up cheating himself.
The last quatrain moves from the counting house to the deathbed. When Nature finally calls him away, what acceptable audit will he be able to present? The couplet answers in the language of wills: "Thy unused beauty must be tombed with thee, / Which, used, lives th' executor to be." A child, in other words, would act as executor of the estate, carrying the beauty forward instead of burying it.
Shakespeare's own literary estate had devoted executors of a sort. In 1623, seven years after his death, his fellow actors and friends John Heminges and Henry Condell published the First Folio, a posthumous collection containing 36 of his plays in a more reliable text than the uneven editions printed while he lived. Its preface carried a poem by his rival Ben Jonson, who praised him as "not of an age, but for all time".
Source: Sonnet 4: Unthrifty loveliness, why dost thou spend
