The “Four-Hymn Mass” began long before the liturgical reforms of Vatican II, as part of the old “Low Mass,” the “silent” Mass in which the priest did all the prayers quietly in Latin while the congregation went about their own devotions.
In the 18th century in Germany, Poland and other countries, the custom began of singing songs in the people’s language during Low Mass, and by the late 19th century this was standard in those areas. Songs were written that mirrored the various parts of the Mass.
Later, in the 1940s, in North America and Northern Europe, the Dialogue Mass developed – still a Low Mass, but with the people responding in Latin to the prayers of the priest, as the servers had done previously. It was at this time that the “Four Hymn Mass” began, with real hymns that made sense for the beginning of Mass, the Offertory, the Communion (now that lay people were encouraged to receive Communion regularly at Mass). The hymn at the end, or the recessional, was borrowed from Protestant practice. There has never been a song officially ending the Roman Rite Mass.
After the reforms of Vatican II, we began to implement the decisions of the world’s bishops about the liturgy, and to sing the Mass, not just sing hymns at Mass. The Mass text itself is sung, and hymns may be sung at particular points. Thus, in a given Mass, we may sing the Entrance or Gathering Song (a psalm or hymn), the Kyrie, the Gloria, the Responsorial Psalm, the Gospel Acclamation, the Intercessions. At the Preparation of the Altar and the Gifts, we may sing a psalm or a hymn, or we may listen to choral or instrumental music, or we may just have silence. The entire Eucharistic Prayer may be sung by the priest, but with the people always singing the Sanctus (Holy), the Memorial Acclamation and the Great Amen. We may sing the Lord’s Prayer and its conclusion (the doxology), the Agnus Dei (Lamb of God), and during Communion a psalm or responsorial song. There is an option for a song of praise after Communion. At the end of Mass, no song is mentioned anywhere in the liturgical documents. It has become the custom in the USA to sing something at this time. This is outside the time of Mass itself, after the final dismissal.
Why have things changed? Over several hundred years, our understanding of the Mass has changed from a private prayer of the priest which people must attend without outward participation, to the most important act of the Body of Christ, gathered together to give thanks to God, to hear God’s Word, to respond in song, to join themselves to the sacrifice of Christ, and to receive the Body and Blood of Christ.
The “Four Hymn Mass” was one brief portion of our journey to recovering the liturgy of the early church in a way that makes sense for people today.