The Lord, desiring that melody be the symbol of spiritual harmony, directed that the psalms be sung rhythmically, that they be chanted. Coupling vocal music to the psalms does not reflect a desire for pleasing sound, but rather betokens the state of harmony of the soul.
St.Athanasius the Great
With melody [sweet singing], the Church adds depth to what is spoken, through which music itself reveals, to the extent possible, the message within the text. It is with this relish, as if with sweetmeats, that savor is imparted to the food of lessons.
Holy Hierarch Gregory of Nyssa
Everything that is in concert with our nature is pleasing to it. And music is in accordance with our nature. For this reason, the great David included sweet singing in the list of learned studies in the virtues. Into exalted dogmas he poured as it were the sweetness of honey, with whose help our nature heals itself. Harmony of life facilitates the healing of our nature, and in my opinion it is sweet-singing that facilitates that harmony. Perhaps it calls us to a an elevated state of life, to the understanding that the disposition of the virtuous should not be coarse, passionate, should not emit too high a sound, like the too tightly wound string which emits an incorrect note. On the other hand, they should not weaken their powers through sensuality, for the sould which is weakened by such passions, turns deaf and dumb. And one must from time to time raise and lower the pitch of one’s soul, in order to always maintain harmony and good order, with neither laxness nor excessive tension.
St. Gregory of Nyssa
Chant is a feast for those who rejoice, comfort to those who despair, a check to those beset by passions. It helps the truth, strikes down abusive intention, kills shameful thoughts, proclaims Divine laws, preaches God, explains the faith, seals off the lips of heretics, and establishes the Church.
St. John Chrysostomos