The Supreme Lord can be pleased only by devotional service: therefore it is said here that the Lord is surely satisfied by devotion and nothing else. Quoting from the Gautamīya-tantra, the Hari-bhakti-vilāsa states:
tulasī-dala-mātreṇa
jalasya culukena vā
vikrīṇīte svam ātmānaṁ
bhaktebhyo bhakta-vatsalaḥ
"Śrī Kṛṣṇa, who is very affectionate toward His devotees, sells Himself to a devotee who offers merely a tulasī leaf and a palmful of water." The Supreme Lord is causelessly merciful upon His devotee, so much so that even the poorest of men can offer Him a little water and a flower in devotion and thus please Him. This is due to His affectionate dealings with His devotees.
(Srimad Bhagavatam------5:3:6------purport).

In the Skanda Purāṇa there is a statement praising the tulasī tree as follows: "Let me offer my respectful obeisances unto the tulasī tree, which can immediately vanquish volumes of sinful activities. Simply by seeing or touching this tree one can become relieved from all distresses and diseases. Simply by offering obeisances to and pouring water on the tulasī tree, one can become freed from the fear of being sent to the court of Yamarāja (the King of death, who punishes the sinful). If someone sows a tulasī tree somewhere, certainly he becomes devoted to Lord Kṛṣṇa. And when the tulasī leaves are offered in devotion at the lotus feet of Kṛṣṇa, there is the full development of love of Godhead."
(Nectar of Devotion).

In the Skanda Purāṇa there is a similar statement: "Persons whose bodies are marked with tilaka, symbolizing the conchshell, wheel, club and lotus—and who keep the leaves of tulasī on their heads, and whose bodies are always decorated with gopī-candana—even seen once, can help the seer be relieved from all sinful activities."
(Nectar of Devotion).

Lord Kṛṣṇa is very fond of tulasī leaves and buds. Because tulasī buds are usually offered up to the lotus feet of Kṛṣṇa, a devotee once prayed to the tulasī buds to give him some information about the lotus feet of the Lord. The devotee expected that the tulasī buds would know something about the glories of Lord Śrī Kṛṣṇa's lotus feet.
(Nectar of Devotion).

Those who are situated on the platform of śānta-rasa get their impetus for advancement in devotional service by smelling the tulasī offered at the lotus feet of the Lord, by hearing the sound of His conchshell, by seeing a sanctified place in some mountain or hill, by observing a forest like the ones in Vṛndāvana, by going to a place of pilgrimage, by visiting the course of the Ganges River, by being victorious over the dictations of bodily demands (i.e., eating, sleeping, mating and defending), by understanding the devastation of eternal time and by constantly associating with devotees engaged in Kṛṣṇa consciousness. All these different items are favorable in elevating saintly persons situated in śānta-rasa to the advanced stage of devotional service.
(Nectar of Devotion).

The gopīs then addressed the tulasī plants: "Dear tulasī, you are much beloved by Lord Kṛṣṇa because your leaves are always at His lotus feet. Dear mālatī flower, dear mallikā flower, dear jasmine flower, all of you must have been touched by Kṛṣṇa while He was passing this way after giving us transcendental enjoyment. Have you seen Mādhava passing this way? O mango trees, O trees of jackfruit, O pear trees and āsana trees! O blackberries and bael trees and trees of the kadamba flower—you are all very pious trees to be living on the bank of the Yamunā. Kṛṣṇa must have passed through this way. Will you kindly let us know which way He has gone?"
(Krsna Book).

Service to the Vaiṣṇava, Tulasī, Ganges and Yamunā are included in pāda-sevanam.
(Srimad Bhagavatam------7:5:23-24------purport).

Kṛṣṇa moves about the forest in the company of His friends, who vividly chant the glories of His magnificent deeds. He thus appears just like the Supreme Personality of Godhead exhibiting His inexhaustible opulences. When the cows wander onto the mountainsides and Kṛṣṇa calls out to them with the sound of His flute, the trees and creepers in the forest respond by becoming so luxuriant with fruits and flowers that they seem to be manifesting Lord Viṣṇu within their hearts. As their branches bend low with the weight, the filaments on their trunks and vines stand erect out of the ecstasy of love of God, and both the trees and the creepers pour down a rain of sweet sap.
Maddened by the divine, honeylike aroma of the tulasī flowers on the garland Kṛṣṇa wears, swarms of bees sing loudly for Him, and that most beautiful of all persons thankfully acknowledges and acclaims their song by taking His flute to His lips and playing it. The charming flute song then steals away the minds of the cranes, swans and other lake-dwelling birds. Indeed they approach Kṛṣṇa, close their eyes and, maintaining strict silence, worship Him by fixing their consciousness upon Him in deep meditation.
(Srimad Bhagavatam------10:35:8-11------translation).

The Lord says in the Bhagavad-gītā (9.26):
patraṁ puṣpaṁ phalaṁ toyaṁ yo me bhaktyā prayacchati
tad ahaṁ bhakty-upahṛtam aśnāmi prayatātmanaḥ
"If one offers Me with love and devotion a leaf, a flower, a fruit or water, I will accept it." Following this principle, Advaita Prabhu pleased the Supreme Personality of Godhead with tulasī leaves and water of the Ganges.
(Sri Caitanya Caritamrta-------1:13:70------purport).

"A person who has no connection with Kṛṣṇa consciousness may be a very great personality in so-called human society, but actually he is no better than a great animal. Such big animals are generally praised by other animals like dogs, hogs camels and asses. A person who does not lend his aural reception to hearing about the Supreme Personality of Godhead must be considered to have earholes like holes in a field. Although that person has a tongue, it is like the tongue of a frog, which unnecessarily creates a disturbance by croaking, inviting the snake of death. Similarly, a person who neither takes advantage of the dust of the lotus feet of great devotees nor smells the tulasī leaves offered to the lotus feet of the Lord must be considered dead even though he is supposedly working."
(Sri Caitanya Caritamrta-------1:13:123------purport).

Once the Catuḥsana Kumāras went to Vaikuṇṭha to visit Nārāyaṇa, the Supreme Personality of Godhead, but they were stopped from entering the palace at the seventh gate by two doorkeepers named Jaya and Vijaya. Due to their jealousy, Jaya and Vijaya would not allow the Kumāras entry, and consequently the Kumāras became angry and cursed Jaya and Vijaya, condemning them to take birth in a family of asuras in the material world. The omniscient Personality of Godhead could immediately understand the incident, and He came with His eternal consort, the goddess of fortune. The Catuḥsana Kumāras immediately offered their obeisances unto the Lord. Simply by seeing the Lord and smelling the aroma oftulasī and saffron from His lotus feet, the Kumāras became devotees and abandoned their long-cherished impersonalism. Thus the four Kumāras were turned into Vaiṣṇavas simply by smelling the aromatic tulasī mixed with saffron.
(Sri Caitanya Caritamrta-------1:17:142------purport).

The word vana means "forest." Vṛndāvana is the name given to the forest where Śrīmatī Vṛndādevī (Tulasīdevī) grows profusely. Actually it is not a forest as we ordinarily consider a forest, because it is very thick with green vegetation. There are twelve such vanas in Vṛndāvana. Some are located on the western side of the Yamunā, and others are on the eastern side. The forests situated on the eastern side are Bhadravana, Bilvavana, Lauhavana, Bhāṇḍīravana and Mahāvana. On the western side are Madhuvana, Tālavana, Kumudavana, Bahulāvana, Kāmyavana, Khadiravana and Vṛndāvana. These are the twelve forests of the Vṛndāvana area.
(Sri Caitanya Caritamrta-------2:17:193------purport).

"Those things which awaken ecstatic love are called uddīpana. Mainly this awakening is made possible by the qualities and activities of Kṛṣṇa, as well as by His mode of decoration and the way His hair is arranged." (B.r.s. 2.1.301) The Bhakti-rasāmṛta-sindhu (2.1.302) also gives the following further examples of uddīpana:
smitāṅga-saurabhe vaṁśa-śṛṅga-nūpura-kambavaḥ
padāṅka-kṣetra-tulasī-bhakta-tad-vāsarādayaḥ
"Kṛṣṇa's smile, the fragrance of His transcendental body, His flute, bugle, ankle bells and conchshell, the marks on His feet, His place of residence, His favorite plant (tulasī), His devotees, and the observance of fasts and vows connected to His devotion all awaken the symptoms of ecstatic love."
(Sri Caitanya Caritamrta-------2:23:51------purport).

The Bhagavad-gītā's process of purifying consciousness is the process of fixing one's mind on Kṛṣṇa by talking of His transcendental activities, cleansing His temple, going to His temple, seeing the beautiful transcendental form of the Lord nicely decorated, hearing His transcendental glories, tasting food offered to Him, associating with His devotees, smelling the flowers and tulasī leaves offered Him, engaging in activities for the Lord's interest, etc.
(Teachings of Lord Caitanya).

King Ambarīṣa fixed his mind on the lotus feet of Lord Kṛṣṇa, engaged his words in describing the abode of the Lord, his hands in cleansing the temple of the Lord, his ears in hearing the pastimes of the Lord, his eyes in seeing the form of the Lord, his body in touching the body of the devotee, his nostrils in smelling the flavor of the flowers offered to the lotus feet of the Lord, his tongue in tasting the tulasī leaves offered to Him, his legs in traveling to the holy place where His temple is situated, his head in offering obeisances unto the Lord, and his desires in fulfilling the desires of the Lord... and all these qualifications made him fit to become a mat-para devotee of the Lord.
(Bhagavad-Gita------2:61------purport).

Simply by tasting the tulasī leaves offered to the lotus feet of the Lord, great sages like Sanat-kumāra became great devotees.
(Bhagavad-Gita------9:2------purport).

One can sow tulasī plants, because tulasī leaves are very important and Kṛṣṇa has recommended this in Bhagavad-gītā. Patraṁ puṣpaṁ phalaṁ toyam. Kṛṣṇa desires that one offer Him either a leaf, or a flower, or fruit, or a little water—and by such an offering He is satisfied. This leaf especially refers to the tulasī. So one can sow tulasī and pour water on the plant. Thus, even the poorest man can engage in the service of Kṛṣṇa.
(Bhagavad-Gita------11:55------purport).

Great sages, such as the four bachelor-devotees Sanaka, Sanātana, Sananda and Sanat-kumāra, were attracted by the fragrance of flowers and tulasī leaves anointed with the pulp of sandalwood offered at the lotus feet of the Lord.
(Srimad Bhagavatam------1:7:10------purport).

The Lord sanctified the River Yamunā from the beginning of His transcendental pastimes in the world. While His father Vasudeva was crossing the Yamunā with the baby Lord Kṛṣṇa for a safe place at Gokula on the other bank of the river from Mathurā, the Lord fell down in the river, and by the dust of His lotus feet the river at once became sanctified. It is especially mentioned herein that Mahārāja Parīkṣit took shelter of that particular river which is beautifully flowing, carrying the dust of the lotus feet of Lord Kṛṣṇa, mixed with tulasīleaves. Lord Kṛṣṇa's lotus feet are always besmeared with the tulasī leaves, and thus as soon as His lotus feet contact the water of the Ganges and the Yamunā, the rivers become at once sanctified.
(Srimad Bhagavatam------1:19:6------purport).

The person who has not at any time received the dust of the feet of the Lord's pure devotee upon his head is certainly a dead body. And the person who has never experienced the aroma of the tulasī leaves from the lotus feet of the Lord is also a dead body, although breathing.
(Srimad Bhagavatam------2:3:23-------translation).

Although flowering plants like the mandāra, kunda, kurabaka, utpala, campaka, arṇa, punnāga, nāgakeśara, bakula, lily and pārijāta are full of transcendental fragrance, they are still conscious of the austerities performed by tulasī, for tulasī is given special preference by the Lord, who garlands Himself with tulasī leaves.
The importance of tulasī leaves is very clearly mentioned here. Tulasī plants and their leaves are very important in devotional service. Devotees are recommended to water the tulasī tree every day and collect the leaves to worship the Lord. One time an atheistic svāmī remarked, "What is the use of watering the tulasī plant? It is better to water eggplant. By watering the eggplant one can get some fruits, but what is the use of watering the tulasī?" These foolish creatures, unacquainted with devotional service, sometimes play havoc with the education of people in general.
(Srimad Bhagavatam------3:15:19-------translation and purport).

Generally, when a woman is kissed by her husband, her face becomes more beautiful. In Vaikuṇṭha also, although the goddess of fortune is naturally as beautiful as can be imagined, she nevertheless awaits the kissing of the Lord to make her face more beautiful. The beautiful face of the goddess of fortune appears in ponds of transcendental crystal water when she worships the Lord with tulasī leaves in her garden.
(Srimad Bhagavatam-----3:15:22------purport).

When the breeze carrying the aroma of tulasī leaves from the toes of the lotus feet of the Personality of Godhead entered the nostrils of those sages, they experienced a change both in body and in mind, even though they were attached to the impersonal Brahman understanding.
It appears from this verse that the four Kumāras were impersonalists or protagonists of the philosophy of monism, becoming one with the Lord. But as soon as they saw the Lord's features, their minds changed. In other words, the impersonalist who feels transcendental pleasure in striving to become one with the Lord is defeated when he sees the beautiful transcendental features of the Lord. Because of the fragrance of His lotus feet, carried by the air and mixed with the aroma of tulasī, their minds changed; instead of becoming one with the Supreme Lord, they thought it wise to be devotees. Becoming a servitor of the lotus feet of the Lord is better than becoming one with the Lord.
(Srimad Bhagavatam------3:15:43-------translation and purport).

O Lord, we pray that You let us be born in any hellish condition of life, just as long as our hearts and minds are always engaged in the service of Your lotus feet, our words are made beautiful (by speaking of Your activities) just as tulasī leaves are beautified when offered unto Your lotus feet, and as long as our ears are always filled with the chanting of Your transcendental qualities.
(Srimad Bhagavatam------2:3:49-------translation).

The example is given here of tulasī leaves. The tulasī leaf is very useful even from the medicinal or antiseptic point of view. It is considered sacred and is offered to the lotus feet of the Lord. The tulasī leaf has numerous good qualities, but if it were not offered to the lotus feet of the Lord, tulasī could not be of much value or importance.
(Srimad Bhagavatam-----3:15:49------purport).

Tulasī leaves are very important in the method of worshiping the Supreme Personality of Godhead. In this verse the word salilaiḥ means "by the water." Of course, Dhruva Mahārāja was worshiping on the bank of the Yamunā. The Yamunā and the Ganges are sacred, and sometimes devotees in India insist that the Deity must be worshiped with water of the Ganges or Yamunā. But here we understand deśa-kāla to mean "according to time and country." In the Western countries there is no River Yamunā or Ganges—water from such sacred rivers is not available. Does this mean that the arcā worship should for that reason be stopped? No. Salilaiḥ refers to any water—whatever is available—but it must be very clear and collected purely. That water can be used. The other paraphernalia, such as flower garlands, fruits and vegetables, should be collected according to the country and according to their availability.
(Srimad Bhagavatam-----4:8:55------purport).