There are two ways of association - by vani and by vapuh. Vani means words and vapuh means physical presence. Physical presence is sometimes appreciable and sometimes not, but Vani continues to exist eternally. Therefore, one must take advantage of the Vani, not the physical presence. (CC, Antya 5 Conclusion)
Next you ask if I am present in my picture and form? Yes. In form as well as in teachings. To carry out the teachings of guru is more important than to worship the form, but none of them should be neglected. Form is called vapu and teachings are called vani. Both should be worshiped. Vani is more important than vapu." (Srila Prabhupada Letter Ahmedabad 14 December, 1972)
Therefore we should take advantage of the Vani, not the physical presence. (Letter to Suci Devi Dasi, 4/11/75)
I shall remain your personal guidance, physically present or not physically present, as I am getting guidance from my Guru Maharaja. (Room Conversation, Vrindavan, 14/7/77)
Physical presence is immaterial. Presence of the transcendental sound received from the Spiritual Master should be the guidance of life. That will make our spiritual life successful. If you feel very strongly about my absence you may place my pictures on my sitting places and this will be source of inspiration for you. (Letter to Brahmananda and other students, 19/1/67)
But always remember that I am always with you. As you are always thinking of me, I am always thinking of you also. Although physically we are not together, we are not separated spiritually. So we should be concerned only with this spiritual connection. (Letter to Gaurasundara, 13/11/69)
So we should associate by vibration, and not by the physical presence. That is real association. (Lectures SB, 68/08/18)
There are two conceptions, the physical conception and the vibrational conception. The physical conception is temporary. The vibrational conception is eternal.[...] When we feel separation from Krsna or the Spirirual Master, we should just try to remember their words or instructions, and we will no longer feel that separation. Such association with Krsna and the Spiritual Master should be association by vibration not physical presence. That is real association. (Elevation to Krsna Consciousness, (BBT 1973), Page 57)
It is sometimes misunderstood that if one has to associate with persons engaged in devotional service, he will not be able to solve the economic problem. To answer this argument, it is described here that one has to associate with liberated persons not directly, physically, but by understanding, through philosophy and logic, the problems of life. (SB 3:31:48 P)
I am always with you. Never mind if I am physically absent. (Letter to Jayananda, 16/9/67)
Paramananda: We're always feeling your presence very strongly, Srila Prabhupada, simply by your teachings and your instructions. We're always meditating on your instructions.
Srila Prabhupada: Thank you. That is the real presence. Physical presence is not important. (Room Conversation, Vrndavana, 6/10/77)
You write that you have desire to avail of my association again, but why do you forget that you are always in association with me? When you are helping my missionary activities I am always thinking of you, and you are always thinking of me . That is real association. Just like I am always thinking of my Guru Maharaja at every moment, although he is not physically present, and because I am trying to serve him to my best capacity, I am sure he is helping me by his spiritual blessings. So there are two kinds of association: physical and preceptorial. Physical association is not so important as preceptorial association. (Letter to Govinda Dasi, 18/8/69)
As far as my blessing is concerned, it does not require my physical presence. If you are chanting Hare Krsna there, and following my instructions, reading the books, taking only Krsna prasadam etc., then there is no question of your not receiving the blessings of Lord Caitanya, whose mission I am humbly trying to push on. (Letter to Bala Krsna, 30/6/74)
Anyone who has developed unflinching faith in the Lord and the Spiritual Master can understand the revealed scripture unfolding before him'. So continue your present aptitude and you will be successful in your spiritual progress. I am sure that even if I am not physically present before you, still you will be able to execute all spiritual duties in the matter of Krsna Consciousness, if you follow the above principles. (Letter to Subala, 29/9/67)
So although a physical body is not present, the vibration should be accepted as the presence of the Spiritual Master, vibration. What we have heard from the Spiritual Master, that is living. (General lectures, 69/01/13)
Devotee: ...so sometimes the Spiritual Master is far away. He may be in Los Angeles. Somebody is coming to Hamburg Temple. He thinks 'How will the Spiritual Master be pleased?'
Srila Prabhupada: Just follow his order, Spiritual Master is along with you by his words. Just like my Spiritual Master is not physically present, but I am associating with him by his words. (SB Lectures, 71/08/18)
Just like I am working, so my Guru Maharaja is there, Bhaktisiddhanta Sarasvati. Physically he may not be, but in every action he is there. To serve master's word is more important than to serve physically. (Room Conversation, Vrindavan, 2/5/77)
So that is called prakata, physically present. And there is another phrase, which is called aprakata, not physically present. But that does not mean, Krsna is dead or God is dead. That does not mean, prakata or aprakata, physically present or not present, it does not matter. (Lectures SB 73/12/11)
So, spiritually, there is no question of separation, even physically we may be in far distant place. (Letter to Syama Dasi, 30/08/68)
I went to your country for spreading this information of Krsna Consciousness and you are helping me in my mission, although I am not physically present there but spiritually I am always with you. (Letter to Nandarani, Krsna Devi and Subala, 3/10/67)
We are not separated actually. There are two - Vani or Vapuh - so Vapu is physical presence and Vani is presence by the vibration, but they are all the same. (Letter to Hamsadutta, 22/6/70)
So in the absence of physical presentation of the spiritual master, the Vaniseva is more important. My Spiritual Master Sarsavati Goswami, may appear to be physically not present, but still because I try to serve his instruction, I never feel separated from him. (Letter to Karandhara, 22/8/70)
I also do not feel separation from my Guru Maharaja. When I am engaged in his service, his pictures give me sufficient strength. To serve master's word is more important than to serve him physically. (Letter to Syamasundara, 19/7/70)
The disciple and spiritual master are never separated because the spiritual master always keeps company with the disciple as long as the disciple follows strictly the instructions of the spiritual master. This is called the association of vani (words). Physical presence is called vapuh. As long as the spiritual master is physically present, the disciple should serve the physical body of the spiritual master, and when the spiritual master is no longer physically existing, the disciple should serve the instructions of the spiritual master. (SB 4.28.47 P)
In conclusion, if a disciple is very serious to execute the mission of the spiritual master, he immediately associates with the Supreme Personality of Godhead by vani or vapuh. This is the only secret of success in seeing the Supreme Personality of Godhead. Instead of being eager to see the Lord in some bush of Vrndavana while at the same time engaging in sense gratification, if one instead sticks to the principle of following the words of the spiritual master, he will see the Supreme Lord without difficulty. (SB 4.28.51 P)