Ṣoḍaśopacāra — The Sixteen Acts of Divine Hospitality
The ṣoḍaśopacāra (ṣoḍaśa = sixteen, upacāra = service/offering) is a widely used framework of sixteen successive ritual acts by which a devotee receives Bhagavān as an honoured guest (atithi) during formal Āgamic pūjā. The sixteen acts correspond directly to the courtesies one would extend to a revered human guest arriving at one's home — elevated into sacred theology by the understanding that Bhagavān is the supreme atithi dwelling in His arcāvatāra form.
One commonly cited list of the sixteen upacāras is: (1) āvāhana — invocation, welcoming the deity's presence into the image or vessel; (2) āsana — offering a seat; (3) pādya — water for washing the feet; (4) arghya — the offering of honour (water, flowers, sandalwood) to the guest's hands; (5) ācamana — water offered for ritual sipping; (6) snāna / abhiṣeka — bathing/anointing the deity; (7) vastra — offering of clothing; (8) yajñopavīta — offering of the sacred thread; (9) gandha — sandalwood paste anointing; (10) puṣpa — flower offering; (11) dhūpa — offering of fragrant incense; (12) dīpa — the waving of a ghee lamp; (13) naivedyam — the food offering; (14) tāmbūla — betel-leaf with areca-nut; (15) nīrājanam / ārati — the ceremonial waving of light; and (16) pradakṣiṇa / namaskāra — circumambulation and prostration.
In Śrī Vaiṣṇava tiruvārādhanam, these services are understood as kaiṅkarya to the Divya Dampati, expressing the jīva's natural śeṣatva and pāratantrya. The Teṉkalai tradition retains this inner orientation while following the actual ārādhana-krama received through the Āchārya. Rāmānuja's Nitya Grantham, for example, organizes worship through connected āsanas and services—arghya, pādya and ācamanīya; snānāsana and tirumañjanam; alaṅkāra-āsana; mantrāsana; bhojyāsana; post-bhojana service; Aruḷicceyal maṅgalāśāsanam; and completion. Therefore the exact upacāra list, order, mantras, eligibility, and use of Divya Prabandham follow the relevant Pāñcarātra or Vaikhānasa Āgama, the Āchārya-paramparā, and the temple or household practice. It is not accurate to state that every item in one sixteenfold list invariably has both a Vedic mantra and a Divya Prabandham pāsuram.