In his “Letter to Marcellinus” the great Athanasius writes these words regarding the value of reciting the Psalms:
Let each one, therefore, who recites the Psalms have a sure hope hope that through them God will speedily give ear to those who are in need. For if a man be in trouble when he says them, great comfort will he find in them; if he be tempted or persecuted, he will find himself abler to stand the test and will experience the protection of the Lord, Who always defends those who say these words. By them too a man will overthrow the devil and put the fiends to fight. If he have sinned, when he uses them he will repent; if he have not sinned, he will find himself rejoicing that he is stretching out towards the things that are before and, so wrestling, in the power of the Psalms he will prevail. Never will such a man be shaken from the truth, but those who try to trick and lead him into error he will refute; and it is no human teacher who promises us this, but the Divine Scripture itself.
I noticed a few things: (1) Athanasius understands the Psalms to have what we may call “devotional” value yet (2) he understand these very Psalms to have doctrinal value (preserving us from error) and elsewhere speaks of the Psalms as being a type of micro-canon containing all the truth of the Hebrew Scriptures in another format. Finally, (3) he sees the Psalms as inspired writing, the words of God, and therefore true in their promise to sustain us.