Walter M. Miller, Jr. was a Roman Catholic, and Catholicism — especially pre-Vatican II Catholicism — infuses A Canticle for Leibowitz.
Contents
Fiat Homo
Fiat homo means "Let there be man" or "Let him become man." This phrase is an allusion to the Nicene creed, Homo factus est, "He became man," or to Genesis, Fiat lux, "Let there be light."
Fiat Lux
Fiat lux means "Let there be light." It is a quote from Genesis chapter 1.
Fiat Voluntas Tua
Fiat voluntas tua means "Thy will be done." It is a quote from the Lord's prayer.
References
List of Latin phrases in A Canticle for Leibowitz Wikipedia(Text) CC BY-SA