Which C.S. Lewis book was published posthumously in 1964 as a fictional correspondence about prayer?

Letters to Malcolm: Chiefly on Prayer was published posthumously in 1964 as a fictional correspondence about prayer. C.S. Lewis had died in 1963, so the book appeared after his death.

The work takes the form of letters addressed to an imagined correspondent named Malcolm. Lewis discusses private and public prayer, worship, silence, church practice, and the difficulties people experience when trying to pray.

The title can mislead readers into expecting a conventional theological treatise. Its epistolary form makes it more conversational, while its subject remains serious and reflective. It is also distinct from A Grief Observed, which focuses on Lewis’s response to Joy Davidman’s death.