I thought this article in Chisa (an Italian newspaper) was very interesting, in its report on a recent 'Study Day' on Sacred Music in Lecce, Italy, attended by some very eminent people, notably Cardinal Walter Brandmüller, president emeritus of the pontifical committee for historical sciences, and Monsignor Valentin Miserachs Grau, President of the Pontifical Institute of Sacred Music. The article summarizes under five headings the talk of the Maestro of a chant choir which is to perform before the Holy Father, Fulvio Rampi.
Rampi defined Chant with five traits, in his talk in Lecce:
1. Gregorian is the chant "proper" to the Latin liturgy. In it, the Church speaks its thought on the Word of God in song.
2. Gregorian is the "sonorous" expression of the interpretation that the Church makes of the Word.
3. Gregorian is not ornamentation, but is itself liturgy.
4. Gregorian is liturgy in its proper times and forms: from the introit to the gradual to the "communio," from the Kyrie to the Agnus Dei.
5. Gregorian is a whole that marks out and embraces the entire liturgical year, intelligible only in its unified vision, like the Sacred Scriptures. It is the musical form of the "lectio divina" of the Church.
Full article here.