The first of Ronald Knox's three "Slow Motion" collections, The Mass in Slow Motion comprises fourteen sermons preached during World War II to the students of the Assumption Sisters at Aldenham Park. Modest yet arresting in style, Knox explains the Mass from the opening psalm to the solemn words of conclusion: Ite missa est. While the liturgy Knox contemplates is that of the Tridentine Rite, the abundant fruits of his contemplation can be easily translated to the Ordinary Form of the present day. Indeed, their primary impetus is the powerful portrayal of the continuous action of the Holy Sacrifice of the Mass, in which formula yields to mystery and man participates in his own salvation.

Along with its "Slow Motion" companions, The Mass in Slow Motion proved the most popular of Knox's writings. Evelyn Waugh called it "the ideal present for a convert of any age or intellectual equipment." More than seventy years since it first appeared in print, the truth of these words holds fast: The Mass in Slow Motion is sure to assist any Catholic-let alone any convert-to more worthily and wisely go up to the altar of the Lord.