As customary, there will be celebrations and somber reflections as American Jews observe the upcoming High Holy Days — their faith’s most important period. There also will be deep disappointment, as rabbis once again cancel or limit in-person worship due to the COVID-19 pandemic. The chief culprit is the quick-spreading delta variant of the coronavirus. Its surge has dashed widespread hopes that this year’s observances, unlike those of 2020, could once again fill synagogues with congregants worshipping side by side. One rabbi in Florida has decided to hold only virtual services for the holy days. Other synagogues are offering a mix of in-person and virtual offerings.