What is an example of the author's use of motif in the novel, Mrs. Osmond?

Throughout Mrs. Osmond, Banville returns to a theater motif in which he compares life to a play. On page 108, for example, he writes of Isabel:

“She had always set a great store by the concept of personal independence: each life is given once, with no possibility of repetition or revision, and the individual actor on whom the vivifying gift is bestowed must play his hour upon the stage with unflagging conviction and in the full realisation that there will be only an opening night, with no “run” to follow.”