The excerpt is from this version online, although if you're going to read it, get the Hayes translation.
Our mental powers should enable us to perceive the swiftness with which all things vanish away: their bodies in the world of space, and their remembrance in the world of time. We should also observe the nature of all objects of sense–particularly such as allure us with pleasure, or affright us with pain, or are clamorously urged upon us by the voice of self-conceit — the cheapness and contemptibility of them, how sordid they are, and how quickly fading and dead. We should discern the true worth of those whose word and opinion confer reputations. We should apprehend, too, the nature of death; and that if only it be steadily contemplated, and the fancies we associate with it be mentally dissected, it will soon come to be thought of as no more than a process of nature (and only children are scared by a natural process) — or rather, something more than a mere process, a positive contribution to nature's well-being. Also we can learn how man has contact with God, and with which part of himself this is maintained, and how that part fares after its removal hence.
Nothing is more melancholy than to compass the whole creation, ‘probing into the deeps of earth' as the poet says, and peering curiously into the secrets of others' souls, without once understanding that to hold fast to the divine spirit within, and serve it loyally, is all that is needful. Such service involves keeping it pure from passion, and from aimlessness, and from discontent with the works of gods or men; for the former of these works deserve our reverence, for their excellence; the latter our goodwill, for fraternity's sake, and at times perhaps our pity too, because of men's ignorance of good and evil–an infirmity as crippling as the inability to distinguish black from white.
Were you to live three thousand years, or even thirty thousand, remember that the sole life which a man can lose is that which he is living at the moment; and furthermore, that he can have no other life except the one he loses. This means that the longest life and the shortest amount to the same thing. For the passing minute is every man's equal possession, but what has once gone by is not ours. Our loss, therefore, is limited to that one fleeting instant, since no one can lose what is already past, nor yet what is still to come–for how can he be deprived of what he does not possess? So two things should be borne in mind. First, that all the cycles of creation since the beginning of time exhibit the same recurring pattern, so that it can make no difference whether you watch the identical spectacle for a hundred years, or for two hundred, or for ever. Secondly, that when the longest-and the shortest-lived of us come to die, their loss is precisely equal. For the sole thing of which any man can be deprived is the present; since this is all he owns, and nobody can lose what is not his.
(h/t Lampham's Quarterly)