“Mar i Cel” is a musical set in 17th-century Spain. It translates as “Sea and Sky”, as a metaphor for a forbidden love between a Muslim and a Christian. Generations have grown up with the musical — which debuted in 1988 — but the show’s handling of religious hatred, exclusion, deportation and generational trauma was ahead of its time. As Alan Ruiz Terol reports from Barcelona, “Mar i Cel’s” current run in Barcelona could be its last.