Bhakti-lata bija

bhakti-latā — of the creeper of devotional service; bīja — the seed
According to their karma, all living entities are wandering throughout the entire universe. Some of them are being elevated to the upper planetary systems, and some are going down into the lower planetary systems. Out of many millions of wandering living entities, one who is very fortunate gets an opportunity to associate with a bona fide spiritual master by the grace of Kṛṣṇa. By the mercy of both Kṛṣṇa and the spiritual master, such a person receives the seed of the creeper of devotional service.
(CC Madhya 19.151)

The ninth chapter describes the desire tree of devotional service. Śrī Caitanya Mahāprabhu Himself is the gardener who planted it.
(CC Ādi 17.322)

All glories to Śrī Mādhavendra Purī, the storehouse of all devotional service unto Kṛṣṇa! He is a desire tree of devotional service, and it is in him that the seed of devotional service first fructified.
(CC Ādi 9.10)

Lord Caitanya likens transcendental devotional service to the sowing of a seed in the heart of the living entity. There are innumerable living entities traveling throughout the different planets of the universe, and out of them there are a few who are fortunate enough to meet a pure devotee and get the chance to understand devotional service. This devotional service is just like a seed, and if it is sown in the heart of a living entity, and if he goes on hearing and chanting Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare, that seed fructifies, just as the seed of a tree fructifies with regular watering. The spiritual plant of devotional service gradually grows and grows until it penetrates the covering of the material universe and enters into the brahma-jyotir effulgence in the spiritual sky. In the spiritual sky also that plant grows more and more until it reaches the highest planet, which is called Goloka Vṛndāvana, the supreme planet of Kṛṣṇa. Ultimately, the plant takes shelter under the lotus feet of Kṛṣṇa and rests there. Gradually, as a plant grows fruits and flowers, that plant of devotional service also produces fruits, and the watering process in the form of chanting and hearing goes on. This plant of devotional service is fully described in the Caitanya-caritāmṛta (Madhya-līlā, Chapter Nineteen). It is explained there that when the complete plant takes shelter under the lotus feet of the Supreme Lord, one becomes fully absorbed in love of God; then he cannot live even for a moment without being in contact with the Supreme Lord, just as a fish cannot live without water. In such a state, the devotee actually attains the transcendental qualities in contact with the Supreme Lord.
(BG 10.29 purport)

Therefore Lord Caitanya said that by the mercy of the spiritual master one can achieve the causeless mercy of the Lord and by the mercy of the Supreme Personality of Godhead one can attain the mercy of the bona fide spiritual master.

Thus by the mercy of the spiritual master and Kṛṣṇa one receives the seed of devotional service. Then one has to sow the seed in the field of his heart, just as a gardener sows the seed of a valuable tree. After sowing this seed, one has to water it by chanting and hearing the holy name of the Supreme Lord and by taking part in discussions about the science of devotional service in a society of pure devotees. When the plant of devotional service sprouts up from the seed of devotion, it begins to grow freely. When it is fully grown, it surpasses the length and breadth of this universe and enters the transcendental atmosphere of the spiritual world, where everything is bathed in the effulgence of the brahmajyoti. The plant penetrates even the brahmajyoti and gradually enters the planet known as Goloka Vṛndāvana. There the plant takes shelter at the lotus feet of Kṛṣṇa. That is the ultimate goal of devotional service. After attaining this position, the plant produces the fruit of love of Godhead. To taste this fruit, however, it is necessary for the devotee, or transcendental gardener, to water the plant daily by chanting and hearing. Unless one waters the plant by chanting and hearing, there is every chance that it will dry up.

Lord Caitanya pointed out to Rūpa Gosvāmī that there was another danger to be encountered while watering the root of the devotional plant. After a plant has grown somewhat, an animal may come and either eat it or destroy it. When the green leaves of a plant are eaten by some animal, the plant generally dies. Thus one has to take precautions so that the plant of devotional service is not disturbed by animals, which represent offenses. The most dangerous animal is a mad elephant, for if a mad elephant enters a garden, it causes tremendous damage to plants and trees. An offense to a pure devotee of the Lord is called vaiṣṇava-aparādha, the mad elephant offense. In the discharge of devotional service, an offense to the feet of a pure devotee creates havoc and stops one’s advancement. Thus one has to defend the plant of bhakti by fencing it off properly and taking care not to offend pure devotees. Then the plant of devotional service will be properly protected.

Other impediments are to desire liberation or material name and fame by discharging devotional service, or to neglect the prohibitions. These prohibitions are mentioned in the authorized scriptures: One should not indulge in illicit sex, intoxication, gambling or eating meat – indeed, one should not eat anything other than kṛṣṇa-prasādam, food offered to Kṛṣṇa. These are the restrictions for one who is attempting to advance in devotional service. If one does not follow these principles strictly, there will be a severe disturbance in the discharge of devotional service.
If one is not particularly careful, by watering the plant of devotional service one will instead nourish the weeds described above, which will then grow very luxuriantly and hamper one’s progress. The idea is that when one waters a garden, not only does the desired plant grow rapidly but the unwanted plants grow also. If the gardener does not see these weeds and cut them down, they will overcome and choke the plant of devotion. It is thus the duty of the neophyte devotee to cut down all the weeds that may grow by the watering process of devotional service. If one is careful to guard against the growth of these weeds, the plant of devotion will grow luxuriantly and reach the ultimate goal, Goloka Vṛndāvana. When the living entity engaged in devotional service relishes the fruit of love of Godhead, he forgets all religious rituals aimed at improving his economic condition. He no longer desires to satisfy his senses, and he no longer desires to become one with the Supreme Lord by merging into His effulgence.
(TLC 1)

As a mad elephant may trample all the plants in a garden, so by committing one offense at the lotus feet of a Vaiṣṇava one may spoil all the devotional service he has accumulated in his life.
(CC Ādi 17.10 purport)