Bob: The guru should be accepted as representative of God?
Prabhupāda: Yes, guru is representative. Guru is the external manifestation of Kṛṣṇa.
Bob: But different than, like the incarnations of Kṛṣṇa that come?
Bob: In what way is the external manifestation of the guru different than the external manifestation of, let us say, Kṛṣṇa or Caitanya when They come to earth.
Prabhupāda: Guru is one, representative of Kṛṣṇa. So there are symptoms who is guru. The general symptoms are described in the Vedas. Tad-vijñānārthaṁ gurum evābhigacchet, śrotriyaṁ brahma-niṣṭham (MU 1.2.12). The first symptom is śrotriyam. Guru is in disciplic succession. One who has thoroughly heard about the Vedas through his spiritual master. This is general description. So another description is in the Bhāgavatam:
- tasmād guruṁ prapadyeta
- jijñāsuḥ śreya uttamam
- śabde pare ca niṣṇātaṁ
- brahmaṇy upaśamāśrayam
- (SB 11.3.21)
Generally, the guru's symptom is that he's a perfect devotee. That's all. And he's serving Kṛṣṇa by preaching His message.