The Narada Bhakti Sutra 84:
य इदं नारदप्रोक्तं शिवानुशासनं विश्वसिति श्रद्धते स भक्तिमान् भवति सः प्रेष्टंं लभते सः प्रेष्टं लभते ।। ८४।।
"One who faithfully accepts these instructions of Lord Shiva as spoken through Nārada becomes a devotee and attains the desired object, attains the desired object."
This verse emphasizes the importance of faith in the spiritual instructions or teachings passed down through a legitimate tradition or Source. Here the reference is to the instructions of Lord Shiva as spoken through the revered saint Narada. By deeply believing and accepting such teachings with faith and surrender, one is able to awaken their innate spirit of Devotion or bhakti. This taking of shelter in the teachings then helps one attain their desired goal or objective, which in the context of these teachings would mean spiritual liberation or moksha.
Having faith in time-tested wisdom aids spiritual progress. It allows one to freely learn and Realize the Truths explained therein. Without such faith, one may question and intellectually challenge in a way that prevents full Realization. Faith here does not mean blind belief but trusting what enlightened Masters have discerned as helpful for elevation of Consciousness. The verse also stresses that by virtue of the devotional attitude developed, one is assured of fulfilling their soul's highest purpose under God's guidance.
In a similar vein, the Yoga Vasistha 6.29.35 states:
अथ यस्य मतिर्मया सहचरति स च मोक्षं लभते ।
यस्य न मतिर्मया सहचरति स भ्रमत्यैव चैव भ्रमति ।।
"One whose intellect moves in harmony with mine attains liberation. But the person whose intellect does not move in harmony with mine simply wanders on confused."
Here the reference is to the enlightened teachings of Sri Vasistha himself. By aligning one's understand with such teachings, liberation is gained, whereas remaining non-receptive leads to continued spiritual wandering and confusion.
Similarly, the Isha Upanishad 3.4 state:
इयं आत्मा सर्वभूतान्तरात्मा । तस्यैवान्वयो जागर्ति सर्वभूतानि । तद्ज्ञानार्थं स्वदर्शनं परमात्मशब्दब्रह्मुपदेशति ।
"This Inner Self is indeed Brahman present in all beings; by its light all beings are illumined. To realize this Inner Self as Brahman Itself, the Upanishads impart this highest instruction through the mahavakya 'Tat Tvam Asi'."
Here faith and receptivity to the Upanishadic teaching helps one recognize their inherent Oneness with the Supreme Reality.
In the first preṣṭam labhate (प्रेष्टंं लभते) – a significant promise that all true devotees will gain their fulfilment of all their honest secular desires and in the repetition of the same pair of words comes an equally ardent promise that all their spiritual desires will also be fully and totally fulfilled. Both these desires are fulfilled for those who live this path of Devotion with faith and sincerity. With his most optimistic promises of the fulfilment of both secular and spiritual joys, the Nārada Bhakti Sūtra concludes.