Bhakti Yoga Swami Vivekananda

...The one great advantage of Bhakti is that it is the easiest, and the most natural way to reach the great divine end in view; its great disadvantage is that in its lower forms it oftentimes degenerates into hideous fanaticism. The fanatical crew in Hinduism, or Mohammedanism, or Christianity, have always been almost exclusively recruited from these worshippers on the lower planes of Bhakti. That singleness of attachment (Nishthâ) to a loved object, without which no genuine love can grow, is very often also the cause of the denunciation of everything else. All the weak and undeveloped minds in every religion or country have only one way of loving their own ideal, i.e. by hating every other ideal. Herein is the explanation of why the same man who is so lovingly attached to his own ideal of God, so devoted to his own ideal of religion, becomes a howling fanatic as soon as he sees or hears anything of any other ideal. This kind of love is somewhat like the canine instinct of guarding the master's property from intrusion; only, the instinct of the dog is better than the reason of man, for the dog never mistakes its master for an enemy in whatever dress he may come before it...

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