Now concerning philosophers, they are of two schools. Thus Socrates the wise believed in the unity of God and the existence of the soul after death; as his opinion was contrary to that of the narrow-minded people of his time, that divine sage was poisoned by them. All divine philosophers and men of wisdom and understanding, when observing these endless beings, have considered that in this great and infinite universe all things end in the mineral kingdom, that the outcome of the mineral kingdom is the vegetable kingdom, the outcome of the vegetable kingdom is the animal kingdom and the outcome of the animal kingdom the world of man. The consummation of this limitless universe with all its grandeur and glory hath been man himself, who in this world of being toileth and suffereth for a time, with divers ills and pains, and ultimately disintegrates, leaving no trace and no fruit after him. Were it so, there is no doubt that this infinite universe with all its perfections has ended in sham and delusion with no result, no fruit, no permanence and no effect. It would be utterly without meaning. They were thus convinced that such is not the case, that this Great Workshop with all its power, its bewildering magnificence and endless perfections, cannot eventually come to naught. That still another life should exist is thus certain, and, just as the vegetable kingdom is unaware of the world of man, so we, too, know not of the Great Life hereafter that followeth the life of man here below. Our non-comprehension of that life, however, is no proof of its non-existence. The mineral world, for instance, is utterly unaware of the world of man and cannot comprehend it, but the ignorance of a thing is no proof of its non-existence. Numerous and conclusive proofs exist that go to show that this infinite world cannot end with this human life (2:16)

End of Quote

Letter to Dr. Forel
'Abdu'l-Baha