As stated in the Brahma-samhitā (5.33):
advaitam acyutam anādim ananta-rūpam
ādyam purāna-purusham nava-yauvanam ca
vedeshu durlabham adurlabham ātma-bhaktau
govindam ādi-purusham tam aham 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 Vishnu. Although Govinda, or Lord Vishnu, 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 Vishnu, Lord Vishnu, Lord Vishnu,” and always think of Lord Vishnu. Vishnor ārādhanam param: this is the highest form of worship. If one remembers Vishnu always, even though one is disturbed by many bad elements, one can be protected without a doubt. The Āyurveda-śāstra recommends, aushadhi cintayet vishnum: even while taking medicine, one should remember Vishnu, because the medicine is not all and all and Lord Vishnu is the real protector. The material world is full of danger (padam padam yad vipadām). Therefore one must become a Vaishnava and think of Vishnu constantly. This is made easier by the chanting of the Hare Krishna mahā-mantra. Therefore Śrī Caitanya Mahāprabhu has recommended, kīrtanīyah sadā harih param vijayate śrī-krishna-sankīrtanam, and kīrtanād eva krishnasya mukta-sangah param vrajet.