“When the Christian confesses to the sin of accidie (that he no longer readily embraces the will of God, that he is lapsing into worldliness, that all the joy has gone out of his communion with God and that he no longer has the strength to pray) it is high time for him to launch an assault upon the flesh, and prepare for better service by fasting and prayer (Luke 2:37, Luke 4:2, Mark 9:29, 1 Corinthians 7:5).”

From Dietrich Bonhoeffer’s The Cost of Discipleship, which is a truly wonderful little book.

You may be interested in the book, The Noonday Devil: Acedia, the Unnamed Evil of Our Times by Abbot Jean-Charles Nault, OSB. He ably and forthrightly treats this subject of acedia that Bonhoeffer opens in the above quote.