The "Stabat Mater," "Tantum Ergo," "Veni, Veni Emanuel," "Ave Maria" and the "Dies Irae" are examples of old Roman Catholic Hymns. Singers in churches and concert halls have traditionally performed and sung these hymns in Latin, because Latin is the traditional language of the Roman Catholic Church and liturgy.
Many believe that St. Thomas Aquinas (1225-1274) composed the words to the "Tantum Ergo." The church uses this hymn for Eucharistic adoration and Benediction of the Blessed Sacrament.
The text of the "Veni, Veni Emanuel" is even older than the "Tantum Ergo," and some scholars date it to the 9th century. The music is of French origin and dates from the 15th century. The text is related to the church's traditional "O Antiphons" that some members of the church sing towards the end of the season of Advent.
The "Stabat Mater" and "Ave Maria" are both old hymns to Mary, the mother of Jesus. The "Stabat Mater" is a meditation on the sufferings of Mary as she watched Jesus die on the cross. Part of the text of the "Ave Maria" comes from the Gospel of Luke 1:28, 42.
The "Dies Irae" was a part of the church's old requiem liturgy for the dead. It is unknown which medieval figure wrote the text.