It was fitting, maybe inevitable, that Yoko Ono and John Lennon met in an art gallery at a showing of her work in London. Now, more than 40 years later, Ms. Ono has established a tradition of exhibiting Mr. Lennon’s art around the United States to celebrate her late husband’s passion for peace and love, which she says with a matter-of-factness that restores those words to their late-1960s meaning, before they became glib catchphrases for many people.