This highly contested question has been debated amongst devotees for decades. Perhaps the following excerpt from a 1971 conversation with Srila Prabhupada in conversation with Dr. Lancelot Ware, the co-founder of the Mensa society (organization of individuals with high IQs), will shed some light on the issue. Please let us know what you think down in the comments.
Syamasundara: But the whole idea is that these personalities have to be in a living form, not just in the past. But they live in the form of a spiritual master who's there to guide us personally—not just praise someone in the past. Unless this process is transmitted in a human form personally, it's not . . .
Prabhupada: That is the process in the material world also. You are lawyer because you have studied laws under some big lawyer. So the process is coming.