Palestrina's Pope Marcellus Mass is purported to have saved polyphony from the Church's chopping block. Its lush, modern sound may be attributed to the use of thirds and sixths. Which is an excerpt of the Kyrie from this Mass?

Some think that the Lord, ten piety is an extension or conclusion of the penitential act; others change it for a song of forgiveness; others, that this invocation is merely penitential, that is, through it, the Lord is asked for forgiveness and nothing else; others simply omit it. In the end you can have some confusion in our defining acclamation. Hence, then, the need to approach the understanding of Kyrie eleison.

The Kyrie eleison is part of the initial rites of the Mass that in its order are made up of the entrance song (1), the initial greeting (2), the penitential act (3), the Lord, have mercy (4), the Hymn of Glory (5) and the Collecting Prayer (6). The purpose of these rites is to provide the assembly for the celebration of the Word and the Eucharist. This purpose of each part of the initial rites, as in the case of Kyrie eleison, has a precise and special meaning, so that while it differs from the others, it achieves the same purpose with them. We discover, then, the origin and evolution of this acclamation within the Christian liturgy.