Main Pesukay D'zimra

One upon a time ago the blog cited from Rashi in Shabbos that the main parts of pesukay d'zimra are the first and third of the hallelujahs.  The question is why are those specifically singled out?  The Toras Avrahom in his mmamer of pisukay d'zimra gives an explanation of this Rashi.  He explains that most mizmorim sing the praises of Hashem.  The focus is on the greatness of G-d and how that is praiseworthy.  These mizmorim are unique because they do not focus on the greatness of G-d but rather on the greatness of man.  It is man who orders all of creation from the tiny ant to the celestial beings and the spiritual forces of angles and heavenly hosts to give praise to Hashem.  The last mizmor describes the arrangement of the shira, the various forms of instruments that should be employed in the symphony.  It is man's recognition of his lack of ability to sing praise to Hashem alone but rather he must use his control over the world to enlist everything in existence to come join in the orchestra of praise to Hashem that is the greatest pisukay d'zimra.  The understanding of the magnitude of the praise that must be given for the day to day miracles of nature that even כל הנשמה תהלל קה, for every נשימה one must praise Hashem.  That is the main avodah of pisukay d'zimra.  That is why Rashi calls these mizmorim specifically pisukay d'zimra for it is by man using his power to acknowledge his lack of ability to thank Hashem on his own that demonstrates the greatest hakarat hatov for the daily nissim.