Following is a compilation of mine regarding the Gaura Gopala Mantra Tattva.
It is (un)fortunately the fact, that we, Nitai-Gaura Naam Bhajan devotees, have to repeatedly face underestimation and minimization of our most dear, Supremely Pure, Eternal and Powerful Holy Names of Lord Gauranga and Nityananda. It happens many times, that Gaura Naam Tattva gets misinterpreted due to lack of knowledge in this regard and due to other considerations as well. It is not surprising for me anymore, as it is a very confindential subject matter, as mentioned by our Seventh Goswami Shrila Shachidananda Bhaktivinoda Thakura in His Shri Navadvipa Dhama Mahatmya (1st Chapter):
aara eka kathaa aache gudha atishaya
kahite na icchaa haya, naa kahile naya..10
"There is one more extremely deep and confidential secret. I do not want to tell it but I cannot remain without describing it as it will supremely benefit all souls."
ihaate aache ta eka gudha-tattva saara
maayaa-mugdha jiva taahaa naa kare vichaara..48
"This mystery of the greatest question and dilemma in the human form of life is not thought about by the souls bewildered by Maya, the illusory energy of the Lord."
What is this secret? It is Gaura-Naam-Lila-Tattva and its supreme importance for the souls of this age of Kali. You can know more about it by reading the whole 1st chapter of Shri Navadvipa Dhama Mahatmya (found in NITAAI Veda). The Glories of Nityananda Gauranga Naam Bhajan, as revealed by our Guru Parampara and Supreme Lord Himself, are unlimited and mentioning them all would definitely exceed the content of this article. However, in the case of further reference and deeper study of this Tattva You the reader is kindly asked to read the book „Nityananda Gauranga Naam", which provides countless evidence and understanding in this regard given by Shrila Prabhupada and our Acharyas.
i beg and pray not to be misunderstood, as it often happens. We, Nitai-Gaura Naam Bhajan devotees, do not want to convert anyone. Chanting of Nityananda Gauranga Naam was never and will never be meant to replace the supremely auspicious and powerful chanting of the Hare Krishna Mahamantra, as preached and advocated by Shri Chaitanya Mahaprahu. Yet, the eternal process of worshiping Lord Gauranga through continuous chanting of His Holy Name, as advocated by our Original Spiritual Master Shriman Nityananda Prabhu, should not be neglected neither. Why not to follow both orders, the one of Lord Gauranga and the one of Lord Nityananda? Both are equally important. In other words, Gauranga Mahaprabhu as well as Radha-Krishna, both are our goals. That means, the eternal process of worshiping them through chanting Their Holy Names is being done simultaneously by the bona-fide school of the followers of Lord Gaurangadeva in the line of Shri Rupa-Vinoda-Saraswati-Gaudiya-Sampradaya. Shrila Prabhupada confirms this point also at various places. Just one of them i mention here:
"It is the advice of Narottama das Thakura to chant the holy name of Gauranga either if one remains at home or in the forest. Similarly, do not forget the chanting of the Hare Krishna mantra either you live in the temple or at home." (Shrila Prabhupada's Letter to: Shachimata, Bombay, 8 December, 1974)
Again You are kindly asked to consult „Nityananda Gauranga Naam" book, attached to this email, which provides further information and quotes for this subject matter.
What i actually wanted to share with You in this email, is the same point, we today during Your lecture. It is the 4-syllable GAURA GOPALA mantra. It stands either for „gau-ra-a-nga" or „ra-dha krish-na" or „ha-re krish-na", depending which of them is being worshiped, Gauranga or Radha-Krishna. Following i am presenting some of the most important quotes describing this Tattva:
Shrila Prabhupada in Cc Antya-lila 2.31 purport:
"Shrila Bhaktivinoda Thakura explains the Gaura-gopala mantra in his Amrta-pravaha-bhasya. Worshipers of Shri Gaurasundara accept the four syllables gau-ra-an-ga as the Gaura mantra, but pure worshipers of Radha and Krishna accept the four syllables ra-dha krs-na as the Gaura-gopala mantra. However, Vaishnavas consider Shri Chaitanya Mahaprabhu nondifferent from Radha-Krishna (shri-krishna-chaitanya radha-krishna nahe anya). Therefore one who chants the mantra "gauranga" and one who chants the names of Radha and Krishna are on the same level."
Purport by Shrila Bhaktivinoda Thakura in his Amrta-pravaha-bhasya to the same verse:
gaura-gopala-mantra-gauravadi gana `gauranga'-name chatura-aksara gaura-mantra ke uddesya karena; kevala krishnavadi gana ei `gaura-gopala-mantra' sabde radha-krsnera chatura-aksara-mantrake uddesya karena.
"The following is the explanation of the Gaura-gopala mantra. The followers of Lord Gaura accept `Gauranga' as the four-syllable mantra and the followers of only Krishna accept `Radha-Krishna' as the Gaura-gopala mantra. The followers of both Lord Gaura and Lord Krishna accept either one of them as the Gaura-gopala mantra understanding that They are non-different from each other."
Shrila Bhaktivinoda Thakura is further revealing the Gaura Gopala Mantra in His classic Jaiva Dharma Chp 14:
vrajanatha: shri gauranga yadi saksat paripurna-tattva hailena, tabe tanhara pujara vyavastha ki?
Vrajanatha: Since Shri Gauranga is the the original complete Absolute Truth, how should one worship Him?
babaji: gauranga-nama mantre gaurapuja karileo yaha haya, krishna-nama-mantre krishna-puja karileo tahai haya. krishna-mantre gaurapuja va gaura-mantre krishnapuja-sakalai eka. ihate je bheda- buddhi kare, se nitanta anabhijna ou kalira dasa.
Babaji: As one worships Lord Krishna by chanting the name and mantra of Krishna, so one should worship Lord Gauranga by chanting the name and mantra of Gauranga. One may worship Lord Gauranga by chanting the Krishna-mantra, or for that matter one may worship Lord Krishna by chanting the Gauranga-mantra. They are all the same. Anyone who thinks Lord Krishna and Lord Gauranga are different is a fool. He is a servant of Kali-yuga.
vrajanatha: channavatarera mantra ki-rupe paoya jaya?
Vrajanatha: Where to obtain the mantras to worship Lord Gauranga who has come as a covered incarnation?
babaji: je tantra prakasya-avataraganera mantra prakasarupe varnana kariyachena, sei tantrei channavatarera mantra channarupe likhiya rakhiyachena. yanhadera buddhi kutila naya, tahara bujhiya laite parena.
Babaji: The scriptures that openly give mantras for worshipping the openly manifested incarnations of the Lord, secretly reveal the mantras (the 4-syllable Gaura-Gopala Mantra, the 6-syllable Gaura Mantra etc) for worshiping the secret and hidden incarnation of Lord Gauranga. People whose intelligence is not crooked can understand and see the presence of these Mantrarajas in the scriptures.
One very interesting purport from Shrila Bhaktisiddhanta Saraswati Thakura Prabhupada in Shri Chaitanya Bhagavata, Adi-lila, 5th Chapter, Verse 125 is further elaborating on the on the importance of worshiping Lord Gaurahari through chanting His Name:
"You invite Me by chanting My mantra, therefore I come and accept the foodstuffs you offer." Some people consider that worshiping and offering foodstuffs to Gauranga is performed by chanting the Gopala-mantra, and by chanting this mantra He accepts the offering. Up to the time when Deity worship of Shri Gaurasundara was introduced in the world, He was worshiped through Krishna-mantras; but after the covered form of Krishna, the origin of all incarnations, mercifully manifested His own form, Deity, and name to His most confidential devotees, the Lord's devotees began to worship the Deity of Shri Gaura by revealing the eternal names and mantras related with Lord Gaura. Those who are bereft of receiving the mercy of the covered incarnation simply make a show of worshiping the Deity form of Shri Gaurasundara with Krishna-mantras, but Shri Gaura is not worshiped in this way. Such people are cheated out of Krishna's mercy, because they do not realize that Gaura's pastimes are eternal.
If one chants Krishna-mantras, then Krishna, or Gaurasundara, accepts his chanting and manifests before the chanter. But if one differentiates between Gaura and Krishna, then his unauthorized endeavors for chanting Krishna-mantras do not qualify him to see the form of Krishna in Gaurasundara and his progress towards freedom from material existence is checked. Therefore it is often found that a worshiper has a lack of taste for worshiping Gaurasundara by chanting Krishna-mantras. Those who do not realize that the worship of Gaurasundara is the same as worship of Krishna are deprived by Shri Ramananda Raya from receiving the mercy of Gaura and the darshana of Gandharvika-Giridhari. Due to the four defects of imperfect senses, the propensity for cheating, certainty of committing mistakes, and certainty of being illusioned, such people are unable to see Shri Radha-Govinda in Shri Gaurasundara. Thus, according to the purport of the second of the four original Bhagavatam verses, such people develop mundane endeavors or vision towards Shri Gaurasundara and become disqualified to see Him. Considering Gaurasundara as different from Krishna, such people with insignificant material vision see Him simply as a sannyasi, a religious reformer, or a pseudo-sentimental saint."
To understand and accept the GAURA GOPALA mantra one shall first try to ontologically understand Lord Gauranga Himself. It is the whole topic for itself and going into that would again exceed the content and objective of this article. But i would like to anyway to at least present one important passage from Jaiva Dharma, where an important basis for correct understanding and acceptance of the bona-fide process of worshiping and attaining Lord Gaurasundara and Radha-Krishna through chanting the Gauranga Mantraraja is given:
Jaiva Dharma, Chapter 17
Vrajanatha: What is the final destination of the soul who is a devotee of Lord Gauranga?
Babaji: Krishna and Gauranga are not different. They are both shelters of the feature of sweetness (madhurya-rasa). They do have one difference. Madhurya-rasa (the Lord's sweetness) has two features: 1. madhurya (sweetness), and 2. audarya (mercy). When sweetness is prominent, Lord Krishna is manifested. When mercy is prominent, Lord Gauranga is manifested. The spiritual world of Vrindavana is divided into two abodes: 1. the abode of Lord Krishna, and 2. the abode of Lord Gauranga. The eternally perfect and eternally liberated souls who have sweetness first and mercy second reside in Lord Krishna's abode. They are Lord Krishna's associates. The eternally perfect and eternally liberated souls who have mercy first and sweetness second reside in Lord Gauranga's abode. They are Lord Gauranga's associates. Some souls manifest two forms and reside in both abodes simultaneously. Other souls manifest only one form and are present in one of the abodes and not in the other. Souls who during the time of sadhana worship only Lord Gauranga, at the time of attaining perfection go to Lord Gauranga's abode and serve Him there. Souls who during the time of sadhana worship only Lord Krishna, at the time of attaining perfection go to Lord Krishna's abode and serve Him there. Souls who during the time of sadhana worship both Lord Krishna and Lord Gauranga, at the time of attaining perfection manifest two forms, go to both Lord Krishna's abode and Lord Gauranga's abode, and in their two forms serve the two Lord's simultaneously in both places. This truth: that Lord Gauranga and Lord Krishna are simultaneously one and different from each other, is a very confidential secret."
So, according to the type of one's attraction, either towards Lord Gaura, Lord Krishna, or both, the Eternal Form of Lord Gauranga and Radha-Krishna are being worshiped through the respective sound of the GAURA GOPALA mantra, speaking „gau-ra-a-nga" or „ra-dha krish-na".
The best is to worship both as done and teached by our Rupa-Vinoda-Saraswati-Gaudiya-Sampradaya and thus attain both the supreme destinationes of Lord Gauranga-Krishna at the time of death.
All credit goes to Shri Nityananda Prabhu, Shrila Bhaktivinoda Thakura and finally my spiritual preceptor Om Vishnupad Shrila Swami Gaurangapada Maharaja, who all of them most mercifully revealed this precious gems of Gauranga-Naam-Lila-Tattva to the suffering souls of Kali Yuga.