Catechesis: Introduction, SC

In the first place, let the preacher above all carefully avoid many versions and various texts and forms of the Ten Commandments, the Lord's Prayer, the Creed, the Sacraments, and such. He should choose one form to which he holds and teaches all the time, year after year. For young and simple people must be taught by uniform settled texts and forms. Otherwise they become confused easily when the teacher teaches them today one way, and in a year some other way, as if he wished to make improvements. For then all effort and labor that has been spent in teaching is lost.—SC Preface 7