Beyond Social Convention
Śuddha-dharma ('pure dharma') refers to the eternal moral and spiritual law flowing from Bhagavān's own nature, as contrasted with laukika-dharma (conventional social morality) or Mīmāṃsā ritual injunctions. The Bhagavad Gītā's Carama Śloka is read as pointing beyond all partial dharmas to śuddha-dharma: complete surrender to Bhagavān as the one unconditioned duty.
Prapatti as Śuddha-Dharma
In Teṅkalai theology, prapatti is characterized as śuddha-dharma — not a socially constituted duty or a means one 'performs,' but the natural expression of the soul's true nature (svarūpa) as the servant and body of Bhagavān. True śuddha-dharma requires no external motivation; it is the soul simply being what it is.
Deśika's Treatment
Vedānta Deśika in Nyāsa Viṃśati uses śuddha-dharma language to distinguish the pure act of surrender (nyāsa) from the ritual frameworks of ordinary karma-kāṇḍa.