In his treatise on Ecclesiastical Offices, Saint Isidore outlines the particular order of prayers in his liturgy. He also details all the hours and all the parts of the canonical office, which are the same as today, and attributes the hymns to Saint Hilary and Saint Ambrose.
In general, several points are found therein that are remarkable with respect to the antiquity of the discipline. Throughout the whole Church, he says, the Eucharist is received while fasting, and the wine must be mixed with water. Also throughout the whole Church, the Sacrifice is offered for the dead, which leaves no room to doubt that this is an apostolic tradition.
Those who have died to grace through sin must do penance before approaching the Sacrament of the altar, and others must not stay away from it for long. Married persons shall observe continence for several days before Communion.
The faithful subjected to public penance shall let their beard and hair grow in disorder, prostrate themselves on sackcloth, and cover themselves with ashes. Penance shall be granted at the end of life, although it is held to be suspect. As for priests and deacons, they shall do penance only before God.
One also sees in the Offices of Saint Isidore the enumeration of the Church's feasts, namely all the Sundays of the year, especially those of Palm Sunday, Easter, Pentecost, Holy Thursday, Good Friday, and Holy Saturday, Christmas, Epiphany, Ascension, the Dedication of Churches, and the feasts of the Apostles and Martyrs, to whom, says the Holy Doctor, we decree not a cult of servitude or latria, since we do not offer the Sacrifice to them, but a cult of charity, in order to obtain the help of their prayers and to excite ourselves to imitate them.
The fasts of the Church were that of Lent, which constitutes the tithe of the year, those of Pentecost and of the Seventh month, that is to say, the Ember Days of summer and autumn. There is no mention of those of winter or December, which were nevertheless in use, at least in Italy, from the time of Saint Leo.
Two other fasts are noted which we no longer practice: one, the cause of which is unknown, on the first day of November, and the other on the first of January, in order to abolish the superstitious debaucheries that the Pagans practiced in honor of Janus.
It is also seen that the Friday fast was then universal, and that most of the faithful joined to it that of Saturday; we have reduced them to abstinence. Saint Isidore takes care to observe that the usages of the Churches are different, and that each one must conform to that in which he lives.
He left us a great number of other writings, the longest and most famous of which, entitled On Origins or Etymologies, was only completed by Saint Braulio of Zaragoza, who divided it into twenty books. It treats of almost all the arts and all the sciences, beginning with grammar, but it gives little more than short definitions, and etymologies which are not always fortunate.
Here, as in all the works of Saint Isidore, one perceives more erudition and labor than taste and invention. His long episcopate, of about forty years, was but a succession of apostolic labors and good works. He died, as he had lived, in the exercise of all episcopal and Christian virtues.
When he believed himself near his end, he so redoubled his almsgiving that for six months his house did not cease to be full of the poor from morning until evening. Feeling his illness increase, he went to the Church of Saint Vincent, followed by an immense crowd of ecclesiastics, religious, and laypeople of every rank, who lamented with great cries.
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At the Church, he stopped in the middle of the choir, before the altar rail, from where he had the women moved aside. Ashes and sackcloth were placed upon him; then, stretching his arms toward Heaven, he renewed himself in sorrow for his sins and received the Body and Blood of Our Lord. After which, he commended himself to the prayers of all present, humbly asked their pardon, discharged his debtors, had the money that remained to him distributed to the poor, and with paternal tenderness, he recommended mutual charity to all his children.
Having then returned to the episcopal house, he died in peace after four days.
Source: History of the Church – Volume Seven – Abbé De Berault-Bercastel – 1781