lessons of the Roman Breviary
May be divided into three groups: scriptural, historical, and patristic.
From Apostolic days the books of Scripture, as well as non-canonical writings, were read in the Christian assemblies.
Considerable diversity existed regarding the choice, number, and length of the scriptural lessons, though undoubtedly their suitability to the various feasts and seasons of the Christian year determined the choice of many of the lessons.
The definite order which emerged in the 4th century and became traditional by the 7th century is still retained in the Roman Breviary.
It is uncertain when scriptural lessons were introduced into the Roman Breviary though we find the traditional order observed in the 7th century.
The scriptural lessons from the Old Testament and New Testament, recited in the first nocturn of Matins, are usually three in number; the three historical lessons, recited in the second nocturn, contain a brief biography of the saint or an account of the feast that is celebrated; the third group of three lessons, recited in the third nocturn, is a homily from one of the Doctors or Fathers of the Church on the Gospel proper to the feast of the day.
The short lesson recited at Prime is generally the same as the Capitulum of None.
New Catholic Dictionary