8 St. Paul showed us clearly that sacred chant was used and held in honor from the very beginning in the Church founded by the Divine Redeemer when he wrote to the Ephesians: "Be filled with the Spirit, speaking to one another in psalms and hymns and spiritual songs." He indicates that this custom of singing hymns was in force in the assemblies of Christians when he says: "When you come together each of you has a hymn."
Source: Musicae Sacrae (Vatican.va)