The loudest cheer at the Jason Isbell show tonight was for a simple verse in the middle of one of his quieter songs, “Cover Me Up”: “I sobered up / I swore off that stuff / Forever this time.” It gave me chills, was one of the strongest moments in a night full of them. His playing, his energy, and all the technical details were spot-on. Clearly we are seeing a man who’s at the pinnacle of his game. But for me, tonight’s performance at the Criterion was defined by how the audience responded to Isbell, how they consider themselves part of his journey to salvation. His songs are clear-eyed, staring into weighty material — addiction, cancer, divorce — with neither drama nor sanguine. Whether you’re drunk or not, Jason Isbell’s songs will sober you up in a hurry.