Humanity has always been a slippery concept. Jan Karski, a Polish diplomat who warned the Allies of genocide only to be ignored and disbelieved, learned this brutal lesson first hand. Masterfully played by David Strathairn, the quietly dignified Karski tells his cautionary tale in “Remember This: The Lesson of Jan Karski.” This harrowing 90-minute solo show, directed by Derek Goldman at Berkeley Repertory Theatre, takes us on an odyssey through the atrocities of the Holocaust. Strathairn may be best known for movies such as “Good Night and Good Luck” and “Nomadland” but the Emmy winner has also shined in many...