The Cosmic PuruSa III

From Purusha SUkta by S.K.Ramachandra Rao, page-72-73:
(...contd from the last post)
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"Even in Yajur Veda, where the references are more obviously to the four social groups, the explanation is symbolic:
as for instance, in Shukla Yajur Veda (14, 28-31), where there is a suggestion that the three currents (prAna, vyAna, and udAna) of the puruSa (or prajApati) represent the brahma, the ten toes, the two thighs, and the torso represent kshatra (viz. the kshtrIyas), the ten vital currents, the five elements, mind, consciousness and ego represent shUdrArye (viz. the SUdrAs and vaishyAs).

References to Brahma and Kshtra are to be found in this Veda quite frequently, and as 'yajamAnAs' in the sacrifical context. Aitareya BrahmaNa states that prajApati created yajna, and after that, brahma and kshatra:

The two [brahma and kshatra] denote powers that make a sacrfice possible. And, according to Satapatha brahmaNa (11.2.7, 16), these two powers are established in the common people, viz. the vaishyAs.

The same text identifies the three factors brahma, kshatra, and vishya with the three vyAhrRtIs-- bhuh (the earth), bhuvah (the midregion) and svah (the sky); PrajApati created the three powers from the three vyAhRtIs.

[Hence] this mantra is to be taken along with other mantras in the context of postulating a common origin for the entire uiverse-- animate as well as inanimate. "

So what is the conclusion?
The whole issue is about sacrifice of puruSa, which can be viewed as a yajna. And brahma and kshatra are two powers that need to be established in vaishyas (common people) or SUdrArye (vaishyAs and SUdrAs) for the success of this yajna.

The only unconnected reference is that the book doesnt not detail any explanation for why the word SUdra is present in only this sUkta in the whole of RV and in what context is it used here.