No psalms composed by private individuals nor any uncanonical books may be read in the church, but only the Canonical Books of the Old and New Testaments.
Notes.
Ancient Epitome of Canon LIX.
Psalms of private origin, or books uncanonical are not to be sung in temples; but the canonical writings of the old and new testaments.
Hefele.
Several heretics, for instance Bardesanes, Paul of Samosata, and Apollinaris—had composed psalms, i.e., Church hymns. The Synod of Laodicea forbade the use of any composed by private individuals, namely all unauthorized Church hymns. Lüft remarks that by this it was not intended to forbid the use of all but the Bible psalms and hymns, for it is known that even after this Synod many hymns composed by individual Christians, for instance, Prudentius, Clement, Ambrose, came into use in the Church. Only those not sanctioned were to be banished.
This idea was greatly exaggerated by some Gallicans in the seventeenth century who wished that all the Antiphons, etc., should be in the words of Holy Scripture. A learned but somewhat distorted account of this whole matter will be found in the Institutions Liturgiques by Dom Prosper Guéranger, tome ij., and a shorter but more temperate account in Dr. Batiffol’s Histoire du Bréviaire Romain, Chap. vj.
Reproduced in full. Translation: Nicene and Post-Nicene Fathers, series 2, vol. 14 (Percival, 1900), public domain (Public domain).