Firstly, this 'until' in boldface is as conjunction, right? I interpret it like this: the soul is polluted day by day, at last it totally believes the truth only exists in a bodily form. But I'm not sure and expecting clearer explanation.
But the soul which has been polluted, and is impure at the time of her departure, and is the companion and servant of the body always, and is in love with and fascinated by the body and by the desires and pleasures of the body, until she is led to believe that the truth only exists in a bodily form, which a man may touch and see and taste, and use for the purposes of his lusts,—the soul, I mean, accustomed to hate and fear and avoid the intellectual principle, which to the bodily eye is dark and invisible, and can be attained only by philosophy;—do you suppose that such a soul will depart pure and unalloyed?
-- Plato's Phaedo 81