Tonight at 6:30 p.m., the president and First Lady Michelle Obama will welcome a handful of friends, staff members and their families into the executive mansion of the White House. The Seder meal will feature a traditional menu of matzo, bitter herbs, a roasted egg and greens, along with the reading of the Haggadah. In a letter to mark the beginning of Passover on Wednesday, Mr. Obama wished Americans a “peaceful and relaxing holiday.” He called the story of the Jewish people’s ascent from slavery to freedom in Israel “among the most powerful stories of suffering and redemption in human history.” “As part of a larger global community,” Mr. Obama wrote, “we all must work to ensure that our brothers and sisters of every race, religion, culture and nationality are free from bondage and repression, and are able to live in peace.”