Aengus had just finished his "Festology," and showed it for the first time to his brother poet, who expressed the warmest approbation of the work.
This composition consists of three parts.

The first part is a poem of five quatrains, invoking the grace and sanctification of Christ for the poet and his undertaking:-- "Sanctify, O Christ! my words: O Lord of the seven heavens! Grant me the gift of wisdom, O Sovereign of the bright sun! "O bright Sun, who dost illuminate The heavens with all Thy holiness! O King, who governest the angels! O Lord of all the people! "O Lord of the people! O King, all righteous and good! May I receive the full benefit Of praising Thy royal hosts.
"Thy royal hosts I praise, Because Thou art my sovereign; I have disposed my mind To be constantly beseeching Thee.
"I beseech a favour from Thee, That I be purified from my sins, Through the peaceful bright-shining flock, The royal host whom I celebrate." Then follows a metrical preface, consisting of eighty stanzas.

These verses are in the same measure[188] as the invocation, Englished by modern Gaedhilic scholars as "chain-verse;" that is, an arrangement of metre by which the first words of every succeeding quatrain are identical with the last words of the preceding one.
After the invocation follows a preface, the second part of this remarkable poem.

In this there is a glowing account of the tortures and sufferings of the early Christian martyrs; it tells "how the names of the persecutors are forgotten, while the names of their victims are remembered with honour, veneration, and affection; how Pilate's wife is forgotten, while the Blessed Virgin Mary is remembered and honoured from the uttermost bounds of the earth to its centre." The martyrology proper, or festology, comes next, and consists of 365 quatrains, or a stanza for each day in the year.
It commences with the feast of the Circumcision:-- "At the head of the congregated saints Let the King take the front place; Unto the noble dispensation did submit Christ--on the kalends of January." St.Patrick is commemorated thus, on the 17th of March:-- "The blaze of a splendid sun, The apostle of stainless Erinn, Patrick, with his countless thousands, May he shelter our wretchedness." On the 13th of April, Bishop Tussach, one of the favourite companions of the great saint, is also mentioned as-- "The kingly bishop Tussach, Who administered, on his arrival, The Body of Christ, the truly powerful King, And the Communion to Patrick." It will be remembered it was from this saint that the great apostle received the holy viaticum.

In the third division of his great work, Aengus explains its use, and directs the people how to read it.
It will be manifest from these poems that the religious principles of the Culdees and of the Irish ecclesiastics generally, were those of the Universal Church at this period.