The Tulsi plant has a significant role in Hinduism and its rituals. It is considered a holy plant, and in front of every Hindu house, there will be a Tulsi plant. Why is it considered a holy plant? What is the textual basis for treating it as holy?
Why is Tulsi considered Sacred
The theological explanation is,
Hindus regard it as an earthly manifestation of the goddess Tulsi, a consort of the god Vishnu. The offering of its leaves is mandatory in ritualistic worship of Vishnu and his forms like Krishna and Vithoba.
While the psychological explanation could be because of the medicinal and antibacterial properties of basil plant,
Tulsi has been used for thousands of years in Ayurveda for its diverse healing properties. It is mentioned in the Charaka Samhita, an ancient Ayurvedic text. Tulsi is considered to be an adaptogen, balancing different processes in the body, and helpful for adapting to stress. Marked by its strong aroma and astringent taste, it is regarded in Ayurveda as a kind of "elixir of life" and believed to promote longevity. It is an elixir for cough; the leaves when chewed after meals acts as a digestive, and when taken before and after cold water bath controls temperature in the stomach and prevents cold. If sprinkled over cooked food in stored water, tulsi leaves prevent bacterial growth.
There are numerous myths and stories of the bond between Tulsi and Krsna (Vishnu), and it's said that Tulsi is the vegetative manifestation of Vishnu.
Tulsi in Hindu scriptures
The Padma Purana declares a person who is cremated with Tulsi twigs in his funeral pyre gains moksha and a place in Vishnu's abode Vaikuntha. If a Tulsi stick is used to burn a lamp for Vishnu, it is like offering the gods lakhs of lamps. If one makes a paste of dried Tulsi wood(from a plant that died naturally) and smears it over his body and worships Vishnu, it is worth several ordinary pujas and lakhs of Godan (donation of cows).Water mixed with the Tulsi leaves is given to the dying to raise their departing souls to heaven.
Just as Tulsi respect is rewarding, her contempt attracts the wrath of Vishnu. Precautions are taken to avoid this. It is taboo to urinate, excrete or throw waste water near the plant. Uprooting and cutting branches of the plant is prohibited. When the plant withers, the dry plant is immersed in a water body with due religious rites as is the custom for broken divine images, which are unworthy for worship. Though Tulsi leaves are necessary for Hindu worship, there are strict rules for it. Only a male must cut them and only in the daylight. A prayer of forgiveness may also be offered to Tulsi before the act.
The esoteric importance: Tulasi as lila-shakti (the pastime energy of the Supreme Lord) is a division of sandhini-shakti (the all-encompasing unifying energy that is the basis of everything). Sandhini-shakti itself is one of the three principal energies of the Lord: sat-cit-ananda.
Tulasi as Vrinda-devi grants one entrance into the ashta-kaliya-lila or the intimate pastimes of Krishna. Neither Brahma, nor Shiva can do that.
One of the best Tulasi experts in the world, Bhakti Visrambha Madhava Swami has collected great original materials on Tulasi (see Books section).
It is considered holy as it has been blessed by Lord Vishnu himself and burns away sins of a person.
Tulasi plant on earth is actually a form of Laxmi. As per Devi Bhagavatam, due to a quarrel among Saraswati, Ganga, Laxmi, Saraswati cursed Laxmi to be born as a plant and river on earth:
brukṣarupā saridrupā bhaviṣyasi na saṃśya
viparītaṃ tato druṣṭvā kiṃcinno vaktumarhasi
saṃtiṣṭhati sabhāmadhye yathā vrukṣo yathā sarit [DB - 9.6.32,33]
Seeing the opposite behavior of Ganga you are not saying anything in this assembly and present as if a tree or river. So you will become the form of a tree and form of river without any doubt.
Laxmi being favorite of Vishnu, He then consoled Her by stating that everything had happened as predestined. So He told Her to go and be born and as a plant in India. She will be known as Tulasi and will be able to purify all the three worlds:
trailokyapāvanīnāmnā tulasīti ca mahābhārate [DB - 9.6.48]
Also, as per Garuda Puran planting, preserving, watering, touching and worshipping Tulasi tree burns away a persons accumulated sins of many births:
तुलसी दहते पापं न्रुणां जन्मार्जितं खग [GP - 2.28.9]
O Bird (Garuda), by planting, preserving, watering, touching and worshipping, Tulasi burns away a person's accumulated sins of many birth.
As per Padma Purana Tulasi is favorite to Krishna or Vishnu. Hence, it is a sacred plant for the Vaishnavas. Wherever Tulasi plant is planted ghosts and demons go away from that place. So due to such reasons it is considered holy and planted in almost every Hindu house.
According to Hindu scripture, the Tulsi plant was a woman named Vrinda (Brinda), a synonym of Tulsi. She was married to the demon-king Jalandhar. Due to her piety and devotion to Vishnu, her husband became invincible. Even god Shiva, the destroyer in the Hindu Trinity could not defeat Jalandhar. So Shiva requested Vishnu - the preserver in the Trinity - to find a solution. Vishnu disguised himself as Jalandhar and tricked Vrinda. Her chastity destroyed, Jalandhar was killed by Shiva. Vrinda cursed Vishnu to become black in colour and he would be separated from his wife. Thus, he was transformed into the black Shaligram stone and in [his Rama] avatar, his wife Sita was kidnapped by a demon-king and thus separated from him. Vrinda then [drowned] herself in the ocean. Eventually Jalandhar was killed by Shiva. The gods or Vishnu transferred her soul to a plant, henceforth which was called as Tulsi.
Another minor legend narrates that Lakshmi - the chief consort of Vishnu - slew a demon on this day and remained on earth as the Tulsi plant.
According to Vaishnavas, it is believed in Puranas that during Samudra Manthana when the gods win the ocean-churning against asuras, Dhanvantari comes up from the ocean with Amrita in hand for the gods. Dhanvantari (the divine medico) sheds happy tears and when the first drop falls in Amrita it forms Tulasi.
That's what the books say, but Tulsi is a herbal plant and is also used for medicinal purposes.