VATICAN CITY — Pope Francis celebrated Palm Sunday Mass without the public because of the coronavirus pandemic, which he said should focus people’s attention on what’s most important, despite heavy hearts — using one’s life to serve others. Looking pensive and sounding subdued, Francis led the first of several solemn Holy Week ceremonies that will shut out rank-and-file faithful from attending, as Italy’s rigid lockdown measures forbid public gatherings. Normally, tens of thousands of Romans, tourists and pilgrims, clutching olive tree branches or palm fronds would have flocked to an outdoor Mass led by the pontiff.