SB 10.6.27-29

As stated in the Brahma-saṁhitā (5.33):

advaitam acyutam anādim ananta-rūpam
ādyaṁ purāṇa-puruṣaṁ nava-yauvanaṁ ca
vedeṣu durlabham adurlabham ātma-bhaktau
govindam ādi-puruṣaṁ tam ahaṁ bhajāmi
“I worship the Supreme Personality of Godhead, Govinda, who is the original person — nondual, infallible, and without beginning. Although He expands into unlimited forms, He is still the original, and although He is the oldest person, He always appears as a fresh youth. Such eternal, blissful and all-knowing forms of the Lord cannot be understood by the academic wisdom of the Vedas, but they are always manifest to pure, unalloyed devotees.”

While decorating the body with tilaka, we give protection to the body by chanting twelve names of Viṣṇu. Although Govinda, or Lord Viṣṇu, is one, He has different names and forms with which to act differently. But if one cannot remember all the names at one time, one may simply chant, “Lord Viṣṇu, Lord Viṣṇu, Lord Viṣṇu,” and always think of Lord Viṣṇu. Viṣṇor ārādhanaṁ param: this is the highest form of worship. If one remembers Viṣṇu always, even though one is disturbed by many bad elements, one can be protected without a doubt. The Āyurveda-śāstra recommends, auṣadhi cintayet viṣṇum: even while taking medicine, one should remember Viṣṇu, because the medicine is not all and all and Lord Viṣṇu is the real protector. The material world is full of danger (padaṁ padaṁ yad vipadām). Therefore one must become a Vaiṣṇava and think of Viṣṇu constantly. This is made easier by the chanting of the Hare Kṛṣṇa mahā-mantra. Therefore Śrī Caitanya Mahāprabhu has recommended, kīrtanīyaḥ sadā hariḥ paraṁ vijayate śrī-kṛṣṇa-saṅkīrtanam, and kīrtanād eva kṛṣṇasya mukta-saṅgaḥ paraṁ vrajet.