There are many parallels between Lee and Luther. Like Lee, Luther also distinguished between scripture which shows us Christ and Scripture which doesn't. Luther wrote:
Let us banish this Epistle from the university, for it is worthless. It has no syllable about Christ, not even naming him except at the beginning. - on the book of James.
"What does not teach Christ is not apostolic, even though St. Peter or St. Paul taught it"
"St. John's Gospel and his first epistle, St. Paul's epistles, especially Romans, Galatians and Ephesians and St. Peter's first epistle [which] are the books that show you Christ and teach you all that is good and necessary for you to know."
Therefore I stick to the books which present Christ to me, clearly and purely . . .
https://www.jesuswordsonly.com/books...and-canon.html
Using Luther's approach, we may say that Lee distinguished between Psalms which "teach Christ" and Psalms which don't.