WHAT IS SRILA GURUDEVA'S ESSENTIAL TEACHING

Śrīla Gurudeva bestows service in the mood of the mañjarīs. One who is not wise in rasa-tattva, who is not present in his spiritual service, can never publish the rasamayī-granthas of the Gosvāmīs. Śrīla Gurudeva is the topmost of rasika and bhāvuka Vaiṣṇavas and is always serving as Śrīmatī Rādhikā’s maidservant. therefore, he revealed the subject matter of mañjarī-bhāva-upāsanā in his books—this subject is essential for one who aspires towards the highest attainment of life. 
sevā sādhaka-rūpeṇa siddha-rūpeṇa cātra hi
tad-bhāva-lsunā kāā vraja-lokānusārataḥ 
The sevaka in his form as a sādhaka serves Hari, Guru and Vaiṣṇavas, and in his internal form is absorbed in bhāva-sevā to Śrī Śrī Rādhā-Kṛṣṇa. Śrīla Gurudeva exemplified bhāva-mārga-sādhana in the eightfold daily pastimes of Rādhā-Kṛṣṇa, and revealed this process in his books. 
Once while staying in Hawaii at the ocean-side home of Vṛndāvana Prabhu, Śrīla Gurudeva went outside to the liu garden and began plucking weeds and picking up twigs. Not seeing Gurudeva inside, his sevakas thought, “Where has Guru Mahārāja gone?” They went to search outside and were surprised to see him, although advanced in years, squatting and tending the garden.
When his sevakas approached and spoke to him, Śrīla Gurudeva startled and returned to external awareness. He then returned inside. Internally, Gurudeva was with the sakhīs making sure there were no thorns on the pathway Kṛṣṇa would take through the forest.
Śrīla Gurudeva explained that when one enters the bhāva-rājya—the realm of ecstatic spiritual service—while in one’s physical body, it is like a wild elephant in a garden. In this example, the body is like the garden and the elephant is bhāva, spiritual ecstasy, that ravagies the physical body. For one’s mortal coil made of material elements cannot tolerate the awakening of transcendental rapture, like a bulb exposed to a higher wattage than it can conduct. A sādhaka who enters the stage of bhāva realizes all Kṛṣṇa’s pastimes in relation to his spiritual service and feels that Kṛṣṇa is calling him, nay, pulling him to Vraja to directly accept his service. One then experiences every moment in this world separated from Rādhā-Kṛṣṇa to be an stage of agony. Worldly people cannot fathom this subject.
People think that Vaiṣṇavas suffer from strokes and different material illnesses. They cannot understand antara-daśā—internal awareness. What can help at that me? Only mahā-saṅkīrtana. Once when Śrīla Gurudeva was in Mathurā, at three-thirty or four a.m. he fell senseless. He would sleep on the veranda. Seeing Gurudeva senseless, we carried him into his room and called for a door. The doctor gave him many types of medicine.
He said Gurudeva had suffered a stroke and gave medicine for him to recover. He also said Śrīla Gurudeva must be given complete rest without any disturbance and without speaking or meeting with anyone. So Gurudeva stayed in his room for three days. After three days, when Gurudeva had recovered, he asked the brahmacārīs, “Why did you stay outside the whole time?” We replied that the doctor had ordered us to do so because he said it was a very dangerous time. Afterwards, the doctor continued to give Gurudeva medicine for many months. When Śrīla Gurudeva spoke the evening of the third day after this incident, then he commented that when aṣṭa-sāttvika-bhāvas manifest in the body, the body cannot tolerate this and starts to fall apart. The bhāvas are like elephants trampling and ravaging a sugarcane field. People think, “The Vaiṣṇava has left this world from a stroke,” or they see any other sickness as the cause of the Vaiṣṇavas’ departure. But advanced Vaiṣṇavas do not pass away from any material cause; it is a transcendental condition. Material doctors have not taken any training in vraja-bhāva and have no relation with the soul. They cannot fathom these transcendental truths of the liberated souls.
The Guru-varga descend from transcendental Vraja to teach the fallen souls the process of vraja-sevā. One who incessantly chants harināma while internally engaged in service in Vraja will soon realize the spiritual form of his Gurudeva along with his own svarūpa and, under guidance of his guru-sakhī, he will become immersed in the bliss of sevā-rasa to Śrī Śrī Rādhā-Mādhava. In this way, absorption in nāma-rasa bears the near of the fruit of prema-rasa. Thus Śrīmatī Rādhikā accepts one as Her maidservant and grants Her prema-sevā.
Otiur me as a sādhaka should mostly be spent engaged in harināma-kīrtana, in high-class sādhu-saṅga, while internally surrendered at
Śrīla Gurudeva’s lotus feet, and always remembering him. Then, at the appropriate time, Śrīla Gurudeva will bring us to eternal Vraja and engage us in prema-sevā. One cannot attain perfection in sādhana while remaining in the association of materialistic people. One’s sādhana will remain lifeless; therefore, high-class sādhu-saṅga is essential. By the mercy of sādhus, one’s heart will be freed from miserliness and poverty of spirit, while spiritual enthusiasm and bliss will swell during the performance of bhajana.
Śrī Guru-pāda-padma is present in his eternal service to Śrī Rādhā-Kṛṣṇa; he comes to this world to show sādhakas the process to achieve Vraja and kṛṣṇa-prema. He is visible in one form in this world, but internally he is always serving in his spiritual form in Vraja. For those who, with a pure conception of his nature and glories, surrender completely to him, Śrī Guru gives darśana of his spiritual form and grants one entrance into Rādhā-Kṛṣṇa’s nitya-sevā.
When Śrī Guru departs, he looks to see who among his followers wants his further association. He thus arranges a place for them to be with him. Those devotees read his teachings and glories. One who serves guru for his pleasure, not his own selfish desires, will soon meet with Śrī Guru again, even after his disappearance. The material and spiritual worlds are distinct and separate. Śrī Guru is transcendental,
and one should endeavor to meet him on that plane through earnest prayer and medtation. He will then accept such service and will protect and maintain such devotees. Impersonalism or voidism has no connection with Śrī Guru; he is eternally present in his spiritual form and he is worshipful and worshipped when manifest in this material world as well as when unmanifest. Śrī Guru does not manifest in that place where disciples do not respect and worship their spiritual master. For this reason, just as the Deity of Bhagavān is established and worshipped in this world, so is the deity of Śrī Guru. Guru accepts worship and prayers of his disciples through his deity form and always protects and supports them. But a disciple who sends off his guru by never thinking of him or serving him becomes a spiritual orphan and an offender to God. Moreover, Śrīla Gurudeva has an eternal relationship with his God family—his godbrothers and disciples—and if one tries to separate them from Śrī Guru or his place, then it is a grave offense. Guru is made glorious by the glories of his followers. He has love and relationship with them all, hence they should be highly regarded and honored.
Through the method of worship in the mood of parakīya performed in Vraja-maṇḍala, Gauḍa-maṇḍala, and Kṣetra-maṇḍala, living entities are attracted to the Supreme Person, Kṛṣṇa. Śrīla Gurudeva established the super-excellence of parakīya-rasa. Śrīla Gurudeva taught: in this worldly life we have mother, father, siblings, relatives, and friends—yet affection for them binds us to material existence. The essence and goal of all knowledge and rules and regulations of scripture is to develop love for Kṛṣṇa and to serve Him. A person who possesses this love and can give this love to others is the best teacher. In this world, love for Kṛṣṇa manifests as parakīya-rasa. When we are amidst all our worldly relations and affairs, bound by so many social duties and customs, and yet we develop the sentiment that this material display is worthless, and love and relationship with Kṛṣṇa is the supreme purpose of life, and we live every moment as an offering to our Eternal Beloved, we approach the true nature of parakīya-rasa. For although there are others who have claims to our love and attention, our mind is attracted at every moment to Kṛṣṇa. Those who think that this world and its people and responsibilities are superior and that Bhagavān and loving service to Him is secondary can never achieve the highest goal of life—pure love in parakīya-rasa.
Even though one may be forced by circumstance to remain in worldly life, if that person there feels that relationship with Kṛṣṇa is of supreme importance, yet he still cannot escape his conditions, but aspires to and endeavors with the best of his ability to develop a connection with God—Kṛṣṇa will then surely soon bring His devotee to the transcendental realm and initiate him into parakīya-rasa-sevā. 
para-vyasaninī nārī vyagrāpi gṛha-karmasu
tad evāsvādaya antar nava-saṅga-rasāyanam
Caitanya-caramrta, Madhya 1.212 
A devotee should remember his relationship with God like a wife who works hard to please the relatives at home so that they do not suspect her of infidelity, while all the time she remembers her paramour and longs to be with him. When there is an intense desire to serve and love Kṛṣṇa and to always be with Him, and one prays always thus for His mercy, then Kṛṣṇa accepts that devoted soul as His beloved and offers her to Śrīmatī Rādhikā to serve Him under Her guidance. This is Śrīla Gurudeva’s essential teaching.
Srila Gurudeva ki Jaya! (excerpted from a Bhaktabandhav book publication, available from; rasik@bhaktabandhav.org )