1 Shmuel טז; יז:א-לז does not compare to later Tehillem in general nor to סז in particular. Why? Primarily due to the T’NaCH/Talmudic common law sh’itta of scholarship. 1 Shmuel טז; יז:א-לז serves as a precedent to Moshe anointing the House of Aaron as Moshiach. Clearly the distinction of the Prophet Shmuel learns the Torah mitzva of Moshiach as לאו דוקא, just as Isaiah referred to king Cyrus as “moshiach”! Tehillim סז limited to the Sinai revelation of mitzvot לשמה as תורה לא בשמים הוא. The sovereignty of 13 tohor middot ה’ ה’ אל רחום וחנון etc restricted unto the Yatzir Ha’Tov within the בכל לבבך. Hence tefillah דאורייתא restricted to the mitzva of kre’a shma wherein a Jew accepts the “yoke of the kingdom of Heaven” ie tohor middot as the dominant guide spirits within his heart. These 13 tohor spirit “middot” referred to as the 13 middot of mercy.
Mitzvot לשמה falsely understood by Goyim who reject the revelation of the Torah at Sinai falsely assume that this critical term refers to “commandments for their own sake”. No such thing as “commandments for their own sake”. All later Torah commandments fall under the heading of the blessing/curse first two Sinai commandments. Hence all commandments לשמה either serve as specifics of blessing or curse/Life or Death.
The mitzva of Moshiach no different from the mitzva of shabbat; both this and that a wisdom/time-oriented positive commandment. Just as shabbat applies to all generations of Israel so to the mitzva of moshiach applies to all generations of Israel. Moshe anointed the House of Aaron as “moshiach”; Shmuel anointed Shaul and David as moshiach; Eliyahu serves as the sign of the moshiach etc etc etc.
The restrictions on tefillah דאורייתא to the mitzvah of Kri’at Shema highlight the expectation of accepting the “yoke of the kingdom of Heaven”; understood as the dominant guiding רוח הקודש middot – Oral Torah – revealed to Moshe following the sin of the Golden Calf word substitution of אלהים for the שמ השם restricted only to judicial judgment of justice in this world by means of מלכות – tohor רוח הקודש middot which rule the Yatzir Ha-Tov within the heart.
Tehillim סז constitutes as a prayer. Prayer by definition not a tefillah blessing because the latter requires swearing an oath inclusive of שם ומלכות preconditions. False oaths attributed to the Floods in the days of Noach. All wisdom commandments/time-oriented mizvot fundamentally and absolutely require k’vanna (שם ומלכות) which Tehillim שבחים/praise fundamentally lack.
1 Shmuel: טז:א-יג does not stand upon its own two feet any more that Gemara halachot. Just as the latter serve to understand the k’vanna of a specific Mishna viewed from a fixed “witness” perspective, so too the Books of the Prophets likewise view Torah commandments from this secondary relationship to Av Torah commandments.
Rabbi Yochanon in mesechta ברכות teaches the halacha that a ברוכה צריך שם ומלכות. Kre’a Shma, the Cohen blessing, the Kadish prayer and the Shemone Esrei all lack שם ומלכות according to the טיפש פשט literal reading of the words.
The pre-condition of שם ומלכות separates wisdom commandments which require k’vanna from תולדות מצוות which do not require k’vanna. The latter secondary commandments serves as בניני אבות by which the generations of Israel can elevate secondary תולדות מצוות to Av tohor wisdom time-oriented commandments. The concept שם depends upon Yovel. Just as Israel slaves in Egypt could not do mitzvot לשמה in g’lut.
Baba Batra 12b specifically instructs that following the sealing of the T’NaCH all future teaching rely upon the masoret of the sealed traditions; “אין נביא רשאי לחדש דברים” . This Talmud serves to reinforce the authority of the written Torah and the Oral Tradition as the permanent guide which determines Jewish culture, tranditions, and life-styles; ensuring that spiritual practices and interpretations remain grounded in the established texts. For example: Rav Saadia Gaon views mitzvot as expressions of Oral Torah divine middot.
Nevu’ah NEVER the source of post g’lut halacha – as codified in both the Mishna and Gemara; anymore than Aggadah serves as the source of Rabbinic Middle Ages Halacha! Rather/אלא the Aggada makes a פרדס דרוש back to NaCH nevu’ah sources to seek the prophetic mussar and to affix this prophetic mussar as the k’vanna of doing halachah as an elevated wisdom\time-oriented commandment from the Torah.