Which C.S. Lewis book was published posthumously in 1964 as a collection of letters and essays?

Letters to Malcolm: Chiefly on Prayer was published posthumously in 1964 as a collection of letters and essays.

The book presents a series of imagined letters from Lewis to a correspondent named Malcolm. Its main subject is prayer, but the letters also discuss church worship, theology, language, and the practical difficulties of Christian belief.

Lewis died in 1963, so the book appeared after his death. It was edited for publication from material he had prepared, and its form differs from a conventional autobiography or systematic theological treatise. The conversational letters allow Lewis to move between personal observations and larger religious arguments.

The title is sometimes confused with A Grief Observed, which was also published under a pseudonym and concerns grief after Joy Davidman’s death. Letters to Malcolm focuses primarily on prayer and was issued posthumously as one of Lewis’s final major religious works.