One does not sing to the Lord by simply uttering the words of the psalm with his mouth, but all who send up the psalmody from a clean heart and who are holy, maintaining righteousness toward God, these are able to sing to God, harmoniously guided by the spiritual rhythms. How many stand there, coming from fornication? How many from theft? How many concealing in their hearts deceit? How many lying? They think they are singing, although in truth they are not singing. For the Scripture invites the saint to the singing of psalms. “A bad tree cannot bear good fruit,” nor a bad heart utter words of life. Therefore, “make the tree good and its fruits good.” Cleanse your hearts, in order that you may bear fruit in the spirit and may be able, after becoming saints, to sing psalms intelligently to the Lord.
"Sing to the Lord, O you saints of His." The prophet seeing these future things, rejoices, and says, "Sing to the Lord, O you saints of His. And make confession of the remembrance of His holiness" [Psalm 30:4]. And make confession to Him, that He has not forgotten the sanctification, wherewith He has sanctified you, although all this intermediate period belong to your desires.
[AD 379] Basil of Caesarea on Psalms 30:4