Every extraordinary power manifesting in creation is but a spark of God's infinite splendor, empowering souls to glorify the Supreme Lord.Listen — Srila Prabhupada Uvaca
Prabhupāda: śaktyāveśāvatāra kṛṣṇera asaìkhya gaṇana dig-daraśana kari mukhya mukhya jana [Cc Madhya 20.367] [”There are unlimited śaktyāveśa-avatāras of Lord Kṛṣṇa. Let Me describe the chief among them.] Lord Caitanya says that incarnation of opulence... Śaktyāveśa avatāra means incarnation of opulence. We have analyzed the opulences of the Supreme Personality of Godhead. So śaktyāveśa avatāra...
An incarnation who represents a particular opulence of the Supreme Lord, he is called śaktyāveśa avatāra. So Lord Caitanya says that there are innumerable incarnations like that, of whom only the principal, I mean to say, principal incarnations, they are mentioned herein. And who are they? 'sanakādi', 'nārada', 'pṛthu', 'paraśurāma', jīva-rūpa 'brahmāra' āveśāvatāra-nāma [Cc Madhya 20.369] [”Some śaktyāveśa-avatāras are the four Kumāras, Nārada, Mahārāja Pṛthu and Paraśurāma. When a living being is empowered to act as Lord Brahmā, he is also considered a śaktyāveśa-avatāra.] Jīva-rūpa 'brahmāra' āveśa.
Brahmā, the first creature of this universe, he's also considered as one of the śaktyāveśa avatāra. Now, so far our experience is concerned, Lord Caitanya says there are innumerable. So how we can accept a avatāra, a śaktyāveśa avatāra, whose names are not mentioned herein? Then we have to...
As in the beginning, Lord Caitanya says that by the symptoms we can understand that He is śaktyāveśa. By the symptoms and activities and influence. So what is that symptom? Symptom is that eternal, and temporary. So avatāra, incarnation, comes to glorify the eternal existence of the Supreme Lord.
So any avatāra, any incarnation, he comes to glorify that "There is spiritual kingdom, there is God, and I have come to reclaim you to back to Godhead, back to home." This is the symptom. So therefore, by that symptom we accept Lord Jesus Christ as śaktyāveśa avatāra, or Hazrat Muhammad, he's also. Because these two religious leaders of the world, they preached about the glorification of the Supreme Lord, and they sacrificed everything for preaching the glories of the Lord. Therefore... And their influence and their followers, there are...
These are the symptoms by which we can understand that Jesus Christ and Hazrat Muhammad was..., were śaktyāveśa avatāras. So far Buddha is concerned, he's also considered śaktyāveśa avatāra. He preached this nirvāṇa philosophy. Although he did not speak about God—because it is considered that he was himself God—but the people amongst whom he preached, they were mostly atheistic people; therefore he did not preach about God. But he did not deny also.
He simply wanted to make extinction of this present worldly activities. That was... Yes. Nirvāṇa.