It is in the nature of the mind to acquire knowledge by the repetition of its experiences. A thought which it is very difficult, at first, to hold and to dwell upon, at last becomes, by constantly being held in the mind, a natural and habitual condition. Just as a boy, when commencing to learn a trade, cannot even handle his tools aright, much less use them correctly, but after long repetition and practice plies them with perfect ease and consummate skill, so a state of mind at first apparently impossible of realization is, by perseverance and practice, at last acquired and built into the character as a natural and spontaneous condition.