In the tradition of Giorgio Morandi and Mark Rothko, Sean Scully’s abstract paintings ply a narrow course that is both emotionally dense and intellectually engaging. Since 1998, Scully has been gradually refining his focus with a group of thematically linked paintings titled “Wall of Light,” inspired by his observation of Mayan ruins. Several dozen oils, watercolors, and pastels from the series, in addition to some earlier works, were recently exhibited at the Phillips Collection, where they revealed a singular achievement, one all the more impressive for its concision. The Irish-born artist,