Returning to museums whose collections we’re well acquainted with is like visiting old friends in their homes. We arrive with a pretty good idea of what we are going to encounter, eager to spend time with those whose company we are sure we will enjoy, in a familiar context. But just as people we’ve known for years can challenge our expectations, museums we frequent often can also offer invigorating surprises. If we are attentive enough (and a painting or sculpture is good enough), it’s possible to discover things we’ve never noticed before in works of art that we think we know thoroughly. Special exhibitions introduce new voices and new ideas, revealing startling connections or equally startling differences by placing paintings and sculptures well known to us in unprecedented contexts, reuniting long-separated relatives or bringing together virtual strangers. New acquisitions and changing installations can shift our sense of the relationships within an established permanent collection—all of which can make us appreciate works of art we’ve looked at for years in fresh ways.

The National Gallery in Washington, D.C. boasts a large, splendid permanent collection that invites and rewards repeat visits. Yet whenever we return, seeking out such favorites as Manet’s Velàzquez-inspired frieze of tenuously related figures, The Old Musician, or Rubens’s enormous, autograph tour de force, Daniel in the Lions’ Den, with its multiple views of the same peevish beast, there is always something unexpected to be found. This summer, in addition to