Explanation of the Prayers and Ceremonies of Holy Mass, Dom Prosper Guéranger - Kyrie

Next follows the Kyrie, which, at a High Mass, is said at the same side of the Altar, where the Introit was read.  The Priest is accompanied by his Ministers, who do not go to the middle of the Altar, until he himself does; meanwhile, they stand behind him, on the steps.  In a Low Mass, the Priest says the Kyrie, in the middle.  This prayer is a cry of entreaty, whereby the Church sues for mercy from the Blessed Trinity.  The first three invocations are addressed to the Father, who is Lord: Kyrie, Eleison; (Lord, have mercy).  The following three are addressed to Christ, the Son incarnate: Christe, eleison.  The last three are addressed to the Holy Ghost, who is Lord, together with the Father and the Son; and therefore, we say to Him also: Kyrie, eleison.  The Son, too, is equally Lord, with the Father and the Holy Ghost: but, holy Church here gives Him the title of Christ, because of the relation this word bears to the Incarnation.  The Choir, too, takes up the same nine invocations; and sings them.  Formerly, it was the practice, in many Churches, to intersperse them with words, which were sung to the same melody as the invocations themselves, as we find in several old Missals.  The Missal of St. Pius the Fifth did away, almost entirely, with these Kyrie, called, on account of these popular additions, Farsati, (in French, farcis).  When the Pope celebrates a Solemn Mass, the singing of the Kyrie is continued during the act of homage which is paid him on his throne: but this is an exception to the present observance throughout the Church.  The three invocations, each repeated thrice over, (as now practised,) are like a telling us of our union, here below, with the nine choirs of Angels, who sing, in heaven, the glory of the Most High.  This union prepares us to join them in the Hymn which is now to follow, and which these blessed Spirits brought down to this our earth.