In the Agnus Dei the circumstances of the time gave him something special to say which has never so imperatively demanded utterance since.
For the various ceremonies in the blessing of the Agnus Dei see A.
It so happens that the supremely important parts of the Mass are those which have the smallest number of words, namely the Kyrie, important as being the opening prayer; the Sanctus and Benedictus, embodying the central acts and ideas of the service; and the Agnus Dei, the prayer with which it concludes.
The mixed chalice was ordered to be used, and the Agnus Dei to be sung during the Communion of the people.
In many parts of Germany the seasons of Lent and Advent are still marked by the use of emblems of mourning in the churches, by the frequency of certain phrases (Kyrie eleison, Agnus Dei) and the absence of others (Hallelujah, Gloria in excelsis) in the liturgical services, by abstinence from some of the usual social festivities, and by the non-celebration of marriages.