From hospital stays to Shabbat dinners, a few lines a day became a Jewish way of reckoning with memory, loss — and the comfort of routine. In January 2011, I wrote my first entry in a five-year diary.

I got back into an old habit one and a half years ago, waiting in the bathroom line at the Lund station in Sweden. The wait had been prolonged due to cleaning, so I took out a pen and notebook that I ...