Advaita, Nityananda, Sri Caitanya Mahaprabhu, Gadadhara, and Srivasa
"Sri Gauranga, Sri Nityananda, Sri Advaita, Sri Gadadhara and Srivasa are all on the same platform, but in spiritually distinguishing between them one should understand that Sri Caitanya Mahaprabhu is the form of a devotee, Nityananda Prabhu appears in the form of a devotee's spiritual master, Advaita Prabhu is the form of a bhakta (devotee) incarnation, Gadadhara Prabhu is the energy of a bhakta, and Srivasa is a pure devotee. Thus there are spiritual distinctions between them."
Caitanya-caritamrta, Adi lila 7:5
"...Although Lord Caitanya Mahaprabhu appeared as a devotee, He is none other than the son of Nanda Maharaja. Similarly, although Sri Nityananda Prabhu appeared as Lord Caitanya's assistant, He is none other than Baladeva, the carrier of the plow. Advaita Acarya is the incarnation of Sadasiva from the spiritual world. All the devotees headed by Srivasa Thakura are His marginal energy, whereas the devotees headed by Gadadhara Pandita are manifestations of His internal potency.
Sri Caitanya Mahaprabhu, Advaita Prabhu and Nityananda Prabhu all belong to the visnu-tattva category. Because Lord Caitanya is an ocean of mercy, He is addressed as mahaprabhu, whereas Nityananda and Advaita, being two great personalities who assist Lord Caitanya, are addressed as prabhu. Thus there are two prabhus and one mahaprabhu. Gadadhara Gosvami is a representative of a perfect brahmana spiritual master. Srivasa Thakura represents a perfect brahmana devotee. These five are known as the Panca-tattva.
Caitanya-caritamrta, Adi lila 17:301
"There is no difference between the energy and the energetic in regard to the Lord's appearance as Sri Caitanya Mahaprabhu and His four associates--Nityananda Prabhu, Advaita Prabhu, Gadadhara, and Srivasa. Amongst these five diverse manifestations of the Supreme Lord (as the Lord Himself and His incarnation, expansion and energies) there is no spiritual difference. They are five in one Absolute Truth. For the sake of relishing transcendental flavors in the Absolute Truth, there are five diverse manifestations. These are called the form of a devotee, the identity of a devotee, the incarnation of a devotee, the pure devotee and devotional energy.
Out of the five diversities in the Absolute Truth, the form of Lord Caitanya is that of the original Personality of Godhead, Krsna. Lord Nityananda is the manifestation of the first expansion of the Supreme Lord. Similarly, Advaita Prabhu is an incarnation of the Supreme Lord. These three--Caitanya, Nityananda and Advaita--belong to the category of Visnu-tattva, or the Supreme Absolute Truth. Srivasa represents the pure devotee, and Gadadhara represents the internal energy of the Lord for the advancement of pure devotion. Therefore Gadadhara and Srivasa, although included in Visnu-tattva, are dependent, diverse energies of the Supreme Lord. In other words, they are not different from the energetic, but they are manifest diversely for the sake of relishing transcendental relationships. The whole process of devotional service involves a transcendental reciprocation in the relationship between the worshiper and the worshiped. Without such a diverse exchange of transcendental flavors, devotional service has no meaning."
Teachings of Lord Caitanya, Chapter 17
In the Srimad-Bhagavatam there is the following statement regarding Sri Caitanya Mahaprabhu:
krsna-varnam tvisakrsnam sangopangastra-parsadam yajhaih sarikirtana-prayair yajanti hi sumedhasah
"In the age of Kali, people who are endowed with sufficient intelligence will worship the Lord, who is accompanied by His associates, by performance of sankirtana yaina." (Bhag. 11.5.32) Sri Caitanya Mahaprabhu is always accompanied by His plenary expansion Sri Nityananda Prabhu, His incarnation Sri Advaita Prabhu, His internal potency Sri Gadadhara Prabhu and His marginal potency Srivasa Prabhu. He is in the midst of them as the Supreme Personality of Godhead. One should know that Sir Caitanya Mahaprabhu is always accompanied by these other tattvas. Therefore our obeisances to Sri Caitanya Mahaprabhu are complete when we say, sri krsna-caitanya prabhu nityananda sri-advaita gadadhara srivas adigaura-bhakta-vrnda. As preachers of the Krsna consciousness movement, we first offer our obeisances to Sri Caitanya Mahaprabhu by chanting this Panca-tattva mantra; then we say, Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare. There are ten offenses in the chanting of the Hare Krsna maha-mantra, but these are not considered in the chanting of the Panca-tattva mantra, namely, sri-krsna-caitanya prabhu nityananda sri-advaita gadadhara srivasadi-gaura-bhakta-vrnda. Sri Caitanya Mahaprabhu is known as maha-vadanyavatara, the most magnanimous incarnation, for He does not consider the offenses of the fallen souls. Thus to derive the full benefit of the chanting of the maha-mantra (Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare), we must first take shelter of Sri Caitanya Mahaprabhu, learn the Panca-tattva maha-mantra, and then chant the Hare Krsna maha-mantra. That will be very effective."
Caitanya-caritamrta Adi-Lila, 7.4
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.