The Supreme Practice for Kali
The Bhāgavata Purāṇam (12.3.51) declares the kali-yuga dharma: kīrtanād eva kṛṣṇasya mukta-saṅgaḥ paraṃ vrajet — "By kīrtana (singing the names) of Kṛṣṇa alone, one attains liberation from material bondage." This verse establishes nāmasaṃkīrtana as the definitive spiritual practice for this age.
The reason: in earlier yugas, other practices were viable (tapas in Satya Yuga, yajna in Tretā Yuga, temple worship in Dvāpara Yuga). In Kali Yuga, with its shortened lifespans, reduced discipline, and general degradation, the chanting of the divine name is the one practice that any person — regardless of qualification — can perform.
The Power of the Name
Sri Vaishnavism holds that the divine name is not merely a symbol pointing to the Lord but is identical with the Lord himself — nāma-nāmī abheda (no difference between the name and the named). This is derived from the Nāmavali Upaniṣad and supported by the Āzhvārs' experience.
The Āzhvārs' songs are themselves nāmasaṃkīrtana — they overflow with divine names, each verse a celebration of the Lord's beauty and qualities. The Viṣṇu Sahasranāmam (thousand names) is the canonical nāmasaṃkīrtana in the Sanskrit tradition.
Collective and Individual
Nāmasaṃkīrtana can be individual (private chanting of mantras and the divine name) or collective (group singing of Divya Prabandham, bhajans in the devotional assembly). Both are meritorious; collective kīrtana (sat-saṅga kīrtana) is especially powerful as it reinforces bhāgavata-sambandha (connection through devotees).