There was never really any risk that James Levine’s rotator cuff injury would affect his conducting skill, of course, but it may be a sign of how important Levine’s presence has been to the revival of the BSO that his return to the podium has inspired such breathless anticipation. “Conducting is a mysterious occupation, one in which the exchange of information seems to occur almost by osmosis. Everyone should be heartened by what happened at Tanglewood on Friday night. No one should worry about Mr. Levine’s arm-waving capacities, nor should they ever have. It is not like losing one’s fastball.”