This intellectual preparation and emotional purification is a task that strains man's faculties to the extreme. Nobody therefore need expect it to be other than a lifetime's task. Few even succeed in finishing it in a single lifetime--a whole series is required in most cases. Nature has taken a very long time to bring man to his present state, so she is in no hurry to complete his development in any particular reincarnation. Yet such is the mystery of grace, that this is always a grand possibility, always the sublime X-factor in every case. But the individual aspirant cannot afford to gamble with this chance, which, after all, is a rare one. He must rely on his personal efforts, on his own strivings, more than anything else, to bring him nearer to the desired goal.
-- Notebooks Category 1: Overview of the Quest > Chapter 5: Self-Development > # 77