The question is about the phrase in which I spoke of the birth of Sri Aurobindo—it was on the eve of his birthday— and I called it an “eternal birth”. I am asked what I meant by “eternal”.
Of course, if the words are taken literally, an “eternal birth” doesn’t signify much. But I am going to explain to you how there can be—and in fact is—a physical explanation or understanding, a mental understanding, a psychic understanding and a spiritual understanding. Physically, it means that the consequences of this birth will last as long as the Earth. The consequences of Sri Aurobindo’s birth will be felt throughout the entire existence of the Earth. And so I called it “eternal”, a little poetically. Mentally, it is a birth the memory of which will last eternally. Through the ages Sri Aurobindo’s birth will be remembered, with all the consequences it has had.
Psychically, it is a birth which will recur eternally, from age to age, in the history of the universe. This birth is a manifestation which takes place periodically, from age to age, in the history of the Earth. That is, the birth itself is renewed, repeated, reproduced, bringing every time perhaps something more—something more complete and more perfect—but it is the same movement of descent, of manifestation, of birth in an earthly body.
And finally, from the purely spiritual point of view, it could be said that it is the birth of the Eternal on Earth. For each time the Avatar takes a physical form it is the birth of the Eternal himself on Earth. All that, contained in two words: “eternal birth”.
Ref: Questions and Answers 1957 – 1958