One of the most important contributions of the Sri Vaishnava Acharyas is the establishment the concept of Ubhaya Vedanta, i.e., the equal validity of both the Sanskrit Sruti (or revealed texts) and the Tamil hymns of the Azhwars (those who had immersed themselves in God and his qualities).
The history behind the concept of ‘Ubhaya-Vedanta’ is most significant for it depicts the way in which the hymns of Azhwars came to be considered as Vedanta in tamil. According to the Acharya Hrudayam, the Vedas as we know are sruti (i.e. what was heard or revealed) and anadi (i.e. without beginning or authorship). They are the supreme authority. The tamil hymns are equally claimed to be “anadi” in the Srivaishnava tradition. They have a ‘beginning’ (adi) from the Azhwars only in the sense that the latter were instruments through which the supreme Lord, Narayana, revealed His will. Like sruti, which was given by the Lord to Brahma, Divya Prabandhams were also given by the Lord to the Azhwars.
Evidence has it that the Azhwars gave equal status to Tamil along with Sanskrit. For instance, Kulasekhara Azhwar in his Perumal Tirumozhi refers to Lord as the northern language, Sanskrit, and the poem of sweet joy in Tamil. Tirumangai Azhwar in his Tirunedunthantakam describes the Lord as one who is in the form of the sound of Tamil (which has the power of expression) and who is in the form of the sanskrit word, vatacol. It is worthy of note here that the Azhwar gives prime importance to Tamil which has felicity in expression and only refers later to sanskrit without any qualifying epithet for the northern language. In the same stanza, Tirumangai Azhwar calls the Lord as the mantra of Vedanta, denoting that all the Upanishads describe only Him. From this, one can glean that the Azhwar is attaching equal significance to Tamil, Sanskrit and Vedanta – who is God Himself, the primordial cause of everything.
Yamunacharya does not refer to Tiruvaimozhi as Dravida Veda but in Stotraratna he does pay homage to the feet of Vakulabharana (Nammazhwar), whom he calls the first Acharya (Stanza-5). Many of Yamuna’s ideas are parallel to those of the Azhwars. It includes for instance, the direct translation from Kulasekhara in stanza 26 of Stotraratna.
Guruparampara records that as part of his temple reforms Ramanuja included the chanting of hymns of the Divya Prabandham. The author of Acharya Hrudayam has recorded that Ramanuja used to explain the Brahmasutras with the aid of Tiruvaimozhi.
That the Divya Prabandhams had been accepted by Srivaishnavas as equivalent to the Sanskrit Vedas as part of regular temple as worship is evident from the reference to Nammazhwar in the Stotras of some of the direct disciples of Ramanuja, like Kuresa and his son, Parasara Bhattar.
Though Nathamunigal and Alavandar were instrumental in introducing the chanting of the Divya Prabandham in Vaishnava temples, it was Ramanuja who systematised and arranged for the chanting of hymns as an integral part of the temple ritual. This is borne out by the inscriptions relating to the post-Ramanuja period. This is also known from the Koyil oluku, which is a recorded document on the Srirangam temple routine from the time of Ramanuja.
Thus, we can see that Emperumanar himself was involved in systematization of Prabandhams and their institutionalization as a temple ritual. Equally, the Azhwars themselves have made liberal references to the sruti texts to explain how they essentially eulogize the same one Lord, Sriram Narayana.
(All information sourced from “Thiruvaimozhi – An English Glossary” (Vol. 1) by Sri. U. ve. Gwalior Sathyamurthi Ayyangar. Emphasis was added by me wherever appropriate.)