Many are aware why Nammazhwars pAsuram is considered to be Baghavad vishayam and that is conveyed very clearly by Swami Parasara Bhattar in his thaniyan, where Swami Nammazhwar is explaning the Artha panjagam in His thiruvoimozhi மிக்க விறைநிலையும் மெய்யா முயிர் நிலையும் தக்க நெறியும் தடையாகித் - தொக்கியலும் ஊழ்வினையும் வாழ்வினையு மோதும் குருகையர்கோன் யாழினிசை வேதத் தியல்
Now let us focus on the thiuvoimozhi's first 21 pAsurams in brief. As Madurakavi Azhwar states, "மிக்க வேதியர் வேதத்தின் உட்பொருள் நிற்கப்பாடி என்நெஞ்சுள் நிறுத்தினான்" Nammazhwar gave the in depth meaning of Vedas in his Thiruvoimozhi and not a mere translation. Not only the content, but the style in which Nammazhwar sung is also similar to Vedas, Upanishads and Vedanta Sutram.....
In the First 10 pAsurams, Nammazhwar tells the nature of Parabrahmam (Ultimate Reality) and not telling who is the paramathma is. Even If we look till the first 20 paasurams, Nammazhwar uses the word avan, ivan and not specific God of any cult. This is the same way how Vedas and even Veda Vyasar in his Brahma Sutram conveys. Vedas or VS first conveys the Nature of Ultimate Reality (Paramathma) without telling the name first....later telling that the parabrahmam is none other than Sriman Narayanan.
Only in the 21st pAsuram Nammazhwar conveys the Parabrahmam as Sriman Narayanan. என்பெருக்கு அந்நலத்து ஒண்பொருள் ஈறில* வண்புகழ் நாரணன் திண்கழல் சேரே - TVM (1.2.10) - 21st pAsuram Swami Nammazhwar conveys that His teachings has a support of the authoritative scriptual texts (vEdappramAnam) - சுடர்மிகு சுருதியுள் உளன் (TVM 1.1.7)
In the very first pAsuram He says that Paramathama is the One who is having Infinite auspicious attributes par excellence (ananta kalyana guna) - உயர்வற உயர்நலம் உடையவன் எவன் அவன்? (TVM 1.1.1) Parabrahmam is the nature of spiritual knowledge and bliss - உணர் முழுநலம் (TVM 1.1.2) and the same pasuram conveys that he is different from cit and acit and can be comprehended by mind cleansed of impurities. He exists in all times and in all places - ஒழிவிலன் பரந்த அந் நலனுடை ஒருவன் (TVM 1.1.3) No one is either higher than Him or equal to Him - எதிர்நிகழ் கழிவினும் இனனில எனனுயிர் மிகுநிரை இலனே (TVM 1.1.2) In TVM 1.1.4 - Nammazhwar conveys that both sentient and non sentient derive their sattaa from paramathma In 1.1.5 - Azhwar conveys that the sustenance of the other two are solely dependent on the paramathma In 1.1.6 - All their activities are controlled by His Sankalpa He abides in everything in the universe as its antarathma and controls them within as well as the organic relation between paramathma and the universe similar to body and soul - உடல்மிசை உயிரெனக் கரந்தெங்கும் பரந்துளன் (TVM 1.1.7) He pervades in everything,in a minute particle of water or earth or ether(TVM 1.1.10) Though He pervades in every particle He is invisible - கரந்தெங்கும் பரந்துளன் (TVM 1.1.7) He is the one who creates and dissolves the Universe - விண்முதல் முழுவதும் வரன் முதலாயவை முழுதுண்ட பரபரன் (TVM 1.1.8) Azhwar sums up all the first 10 pAsurams and upholds the theory that Brahman is 'Savisesha' as against 'nirvisesha'.
Similarly in the other 10 pAsurams the rest of the facts of the artha panjagam like the nature of jivathma and ways to attain moksha are given as a quintessence. and then the 21st convey the one who possess those divine attributes and the one without second par excellence is none other than Sriman Narayanan (1.2.10) Thus it is very firmly concluded that the first 20+1 pAsurams covers the essential details of the artha panjagam esp the first 10 pasurams cover the detail of Ultimate reality in a good level. This aided Baghavat Ramanujar to compose His Magnum Opus Sri Bashyam and also in demolishing the wrong interpretations by other siddhanthams. Acharyan thiruvadigalae saranam!!