As stated in the Foreword of his first completed volume (Vol. III in 1946), Fr. Weller compiled his set of The Roman Ritual for the clergy "as a manual and reference" and for the laity's "interest and enthusiasm for the rites and prayers of so important a part of the liturgical books of the Church."

His indispensable 3-volume set was especially prized for its thoroughness in treating of the liturgical laws pertaining to each rite, as well as his copious and instructive commentaries.