We are living in a golden age of both fretting about handwriting and fetishizing it. Polemicists lament that cursive is going the way of the dodo. Meanwhile, old-school devotees of pen and paper post their work on social media with hashtags like #snailmail and #penpal.

“The Magic of Handwriting,” an exhibition at the Morgan Library & Museum in New York, might seem at first glance to be part of this nostalgia. Instead, it simply luxuriates in the humble, intimate and sometimes very messy traces that some of the great figures of history have left behind.

The show features some 140 items from the encyclopedic holdings of the Brazilian collector Pedro Corrêa do Lago, who got his start at the age of 11, when he wrote to prominent figures to ask for their autographs. Today, he owns roughly 100,000 letters, notes, receipts, manuscripts, signed photographs and other pieces documenting notable lives in the arts, politics, science and other fields.

During an interview at the museum, the relentlessly loquacious Mr. Corrêa do Lago, 60, called his collection “a symbolic snapshot of Western culture over the past 500 years.” He also sees it as the product of a kind of madness. “It became an absolutely crazy project that drowned all the money I made,” he said, with a laugh. “I should be in a straitjacket.”