Editing Shabbos Mevarchim (section)

==== Reasons for the Takana ====
Shabbos Mevorchim is a general day that influences blessing for all days of the month, as in the text of Birchas HaChodesh said on this Shabbos: "Renew for us this month for good and for blessing, for joy and for gladness, for salvation and for consolation." The drawing down of the blessing depends on making a vessel below, and saying all of Tehillim on this Shabbos is the vessel that prepares and gives strength for the blessing to work and influence successfully all days of the month. Tehillim is a vessel for drawing down Hashem's blessing for all days of the month.

Therefore on Shabbos Mevorchim we say Tehillim before Shacharis, unlike the daily Tehillim recitation which is after davening, because the goal is to affect additional strength in Birchas HaChodesh said during davening.

Why wasn't the takana to say Tehillim on Rosh Chodesh which, as its name implies, is a general day that includes all days of the month and leads and influences them like the head leads and influences the entire body?

First - saying Tehillim on Shabbos Kodesh works and influences much more. Second - to a certain extent Shabbos Mevorchim is a general day, whose influence on all days of the month is stronger and more significant than the influence of Rosh Chodesh. In other words: Shabbos Mevorchim is a greater general principle than Rosh Chodesh, and "all days of the month exist in Shabbos Mevorchim with more refinement and elevation than they exist in Rosh Chodesh itself."

This is because it essentially influences all days of the month in two ways:

# Direct influence from it to all days of the month
# Since Rosh Chodesh is on one of the weekdays that are blessed from it, it influences indirectly through Rosh Chodesh on all days of the month.

Therefore there is maximum importance to say all Tehillim on Shabbos Mevorchim before davening, as this influences tremendous blessing on all the coming days of the month for good.