1 Corinthians 14:15:“What is the conclusion then? I will pray with the spirit, and I will also pray with the understanding. I will sing with the spirit, and I will also sing with the understanding”
Prayer Beyond Psalmody. Abraham of Nathpar: It is in spirit and mind that one should pray and sing to God. Paul does not say anything about the tongue. The reason is that this spiritual prayer is not offered up or prayed by the tongue, for it is deeper than the lips and the tongue, more interiorized than any composite sounds, lying beyond psalmody and wisdom.
Sing with the Spirit. Cassiodorus: The prayer of those who sing is acceptable to God only if a pure heart carries the same message which the words of the hymn unfold.
Origen: “But he that asketh must do everything in his power that he may pray “with the spirit” and pray also “with the understanding”