The Psalms bring in the idea of experience with our Lord. The soul has had to do with Him. There are depth, gravity and dignity—features which can be observed by others.
What choice expressions of soul-appreciation we get. “Thy word have I hid in mine heart, that I might not sin against Thee.” “Open Thou mine eyes, that I may behold wondrous things out of Thy law.” “Turn away mine eyes from beholding vanity.”
The Psalms have to do especially with what is moral—showing that all the experiences of life, if gone through with the Lord, would result in moral conformance to Himself and an intense love for the things He loves.
From a personal letter