AapaathacUdamanubhUya harim shyaanam
madhyE kavErathuhithurmuthithaantharaathmaa |
athrashtruthaam nayanayor vishayaantharaaNaam
yo nishcikaaya manavai munivaahanam tam ||

Meaning
That person (ThiruppaaNaazhvaar), who has (LOkasaaranga) rishi as his vehicle, who immersed himself from the feet to the head of Hari (Ranganatha) - who rests in the middle of the Kaveri river; and who declared that his eyes would see nothing else, on him I set my mind.

Excerpt from piLLailOkam jeeyar's vyaakyaanam
The unseeable (paramapathanaathan) is in the seen (archaavataaram - periya perumaaL). Aazhvaar saw from the feet to the head (AapaathacUdam - thiruppaathakEsam). Once he thus saw, he became a person who never saw anything else again (athrashtruthAm nayanayOr vishayaantharaaNaam).

Brahma saw with all his four heads, while aazhvaar saw with one head (two eyes). Brahma saw from the head to the toe and delighted in that (kirItakEyUraka rathnakuNdalam ...); while aazhvaar being an adiyaar started from the feet (adiyilirinthu thodankinaar).

Periyaazhvaar delighted in Krishnaavataaram, while ThiruppaaNaazhvaar delights in archaavataaram. In this experience, they are thus like brothers.

Periyaazhvaar	ThiruppaaNaazhvaar
paathakamalam	thirukkamalapaatham
peethakacciRRaadaiyOdum	araiccivanthavaadaiyinmEl
azhakiyavunthiyai	ayanaippadaiththathOrezhilunthi
pazhanthaampaalaarththavutharam	thiruvayiRRutharapantham
kurumaamaNippooN ulaavith thikazhum thirumaarvu	thiruvaaramaarvu
aNdamum naadum adanka vizhunkiya kaNdam	muRRumuNda kaNdam
neyththala nEmiyum sankum nilaaviya kaiththalam	kayinAr surisankanalaazhiyar
senthoNdaivaay	seyyavaay
kaNkaLirunthavaa	apperiyavaaya kaNkaL
uruvukariyavoLi maNivaNNan	ezhil neela mEni
kuzhalkaLirunthavaa	thuLavaviraiyArkamazh neeNmudi

kaattavE kaNda paathakamala nallaadaiyunthi
thEttaru mutharapanthath thirumaarvu kaNdanj sevvaay
vaattamil kaNkaLmEni muniyERith thanipukunthu
pAttinaal kaNduvaazhum paaNarthaaL paravinOmE

Meaning
We salute the feet of ThiruppaaNaazhvaar, who climbing on the shoulders of the Muni (LOkasaaranga rishi) went by himself inside (the temple) and saw what was shown, which were the lotus feet, the dress, the navel, the golden waist chain that is difficult to obtain, the chest where Sri resides, the neck, the red lips, the eyes that never tire, the body (that houses all the above), and saw the above through songs.

The two phrases to watch in this taniyan are: kaattavE kaNda and paattinaal kaNdu.

kaattavE kaNda
Saw what was shown. Who showed these to AzhvAr - was it the rishi who took him inside the temple, or, as it must have happened, periya perumaaL showed Himself to Aazhvaar. We have to realize that while most of us go to SriRangam and worship Ranganatha, we only see the arcaavataram of emperumaan. On the other hand, Aazhvaar not only saw the arcaavataaram, but also was shown His divyamangalarUpam by Sriman Narayana.

paattinAl kaNdu
Saw through songs. Everyone sees SriRanganatha. But it was given only to Aazhvaar to see Him through a song.

Did Aazhvaar just see emperumAn? No, he saw Him when he was shown by Him. Did he then just see what was shown; no, he saw what was shown through a song.