Pope Francis celebrated Easter Sunday Mass in St. Peter’s Square for the first time since the coronavirus pandemic, making Christianity’s most joyous day at a time when the war in Ukraine has weighed heavily on his heart. The pontiff, who has a knee ligament problem, limped badly as he stepped out from the back of St. Peter’s Basilica to reach an altar set up on the steps outside, shaded by a canopy against brilliant sunshine. Tens of thousands of people, numbered at 50,000 by the Vatican, many in shirt sleeves, packed the flower-bedecked square and a nearby boulevard to hear his words. After …