The Śrī Sūktam is the oldest, most authoritative Vedic invocation of the Divine Mother known to the Sanātana tradition. It is preserved in the Khila portion of the Ṛgveda — the appended sūktas that the Vedic tradition itself recognizes as smṛti-validated śruti, recited with the same sanctity as the principal maṇḍalas. The Ṛṣi is traditionally given as Ānanda (or Śrī); the chandas vary across the sixteen ṛks (anuṣṭubh, triṣṭubh, jagatī); the devatā throughout is Śrī Mahālakṣmī.
What makes this sūkta unique is that it is the place where the Veda itself directly identifies Śrī as the supreme feminine principle worthy of invocation. The opening ṛk — hiraṇyavarṇāṃ hariṇīṃ suvarṇarajatasrajām — does not describe a minor devatā. It describes the One who is golden-hued, garlanded in gold and silver, radiant as the moon, whom the worshipper asks Agni Jātavedas to bring into his life. Every later stotra of Lakṣmī, from the Purāṇas through the Pāñcarātra Āgamas through the Stuti compositions of Vedānta Deśika, draws its authority from these sixteen verses.
In Śrīvaiṣṇava household practice the Śrī Sūktam opens every nitya-karma. It is recited at the morning sandhyā, before every yajña, at the beginning of every saṃskāra from upanayana to vivāha, and as the central invocation of the Friday Lakṣmī Pūjā. Pāñcarātra liturgy places it at the head of every Lakṣmī ārādhana before the deity is bathed, robed, or fed.
The doctrinal place of this sūkta in our Sampradāya rests on the puruṣakāra teaching. Bhagavad Sri Rāmānujācārya taught that no soul approaches the Lord except through the mediation of Śrī. The Śrī Sūktam enacts this principle in mantra form: the worshipper does not address Lakṣmī directly but asks Agni — the inner antar-yāmin who carries every offering — to bring Her near. He performs prapatti to the Mother first, that She may receive him. Sixteen verses to invoke the One through whom all other invocations succeed.