Fifthly, the soul, if not outwardly arrested by some hostile agent, seems capable of endless progress without ever exhausting either its own capacity or the perfections of infinitude.18 There are before it unlimited truth, beauty, power, nobleness, to be contemplated, mastered, acquired. With indefatigable alacrity, insatiable faculty and desire, it responds to the infinite call. The obvious inference is that its destiny is unending advancement. Annihilation would be a sequel absurdly incongruous with the facts. True, the body decays, and all manifested energy fails; but that is the fault of the mechanism, not of the spirit. Were we to live many thousands of years, as Martineau suggests, no one supposes new souls, but only new organizations, would be needed. And what period can we imagine to terminate the unimpeded spirit's abilities to learn, to enjoy, to expand? Kant's famous demonstration of man's eternal life on the grounds of practical reason is similar. The related ideas of absolute virtue and a moral being necessarily imply the infinite progress of the latter towards the former. That progress is impossible except on condition of the continued existence of the same being. Therefore the soul is immortal.19 Sixthly, our whole life here is a steady series of growing preparations for a continued and ascending life hereafter. All the spiritual powers we develop are so much athletic training, all the ideal treasures we accumulate are so many preliminary attainments, for a future life. They have this appearance and superscription. Man alone foreknows his own death and expects a succeeding existence; and that foresight is given to prepare him. There are wondrous impulses in us, constitutional convictions prescient of futurity, like those prevising instincts in birds leading them to take preparatory flights before their actual migration. 18 Addison, Spectator, Nos. 3 and 210. 19 Jacob, Beweis fur die Unsterblichkeit der Seele aus dem Begriffe der Pflicht. Eternity is the stuff of which our love, flying forward, builds its nest in the eaves of the universe. If we saw wings growing out upon a young creature, we should be forced to conclude that he was intended some time to fly. It is so with man. By exploring thoughts, disciplinary sacrifices, supernal prayers, holy toils of disinterestedness, he fledges his soul's pinions, lays up treasures in heaven, and at last migrates to the attracting clime. "Here sits he, shaping wings to fly: His heart forebodes a mystery; He names the name eternity."