From Chapter IX of Bhakti-Yoga of Volume 3 of Complete Works of Swami Vivekananda.
The next thing to be considered is what we know as Ishta-Nishthâ. One who aspires to be a Bhakta must know that “so many opinions are so many ways”. He must know that all the various sects of the various religions are the various manifestations of the glory of the same Lord. “They call You by so many names; they divide You, as it were, by different names, yet in each one of these is to be found Your omnipotence….You reach the worshipper through all of these, neither is there any special time so long as the soul has intense love for You. You are so easy of approach; it is my misfortune that I cannot love You.” Not only this, the Bhakta must take care not to hate, nor even to criticise those radiant sons of light who are the founders of various sects; he must not even hear them spoken ill of. Very few indeed are those who are at once the possessors of an extensive sympathy and power of appreciation, as well as an intensity of love. We find, as a rule, that liberal and sympathetic sects lose the intensity of religious feeling, and in their hands, religion is apt to degenerate into a kind of politico-social club life. On the other hand, intensely narrow sectaries, whilst displaying a very commendable love of their own ideals, are seen to have acquired every particle of that love by hating every one who is not of exactly the same opinions as themselves. Would to God that this world was full of men who were as intense in their love as worldwide in their sympathies! But such are only few and far between. Yet we know that it is practicable to educate large numbers of human beings into the ideal of a wonderful blending of both the width and the intensity of love; and the way to do that is by this path of the Istha-Nishtha or “steadfast devotion to the chosen ideal”. Every sect of every religion presents only one ideal of its own to mankind, but the eternal Vedantic religion opens to mankind an infinite number of doors for ingress into the inner shrine of divinity, and places before humanity an almost inexhaustible array of ideals, there being in each of them a manifestation of the Eternal One. With the kindest solicitude, the Vedanta points out to aspiring men and women the numerous roads, hewn out of the solid rock of the realities of human life, by the glorious sons, or human manifestations, of God, in the past and in the present, and stands with outstretched arms to welcome all — to welcome even those that are yet to be — to that Home of Truth and that Ocean of Bliss, wherein the human soul, liberated from the net of Mâyâ, may transport itself with perfect freedom and with eternal joy.
Bhakti-Yoga, therefore, lays on us the imperative command not to hate or deny any one of the various paths that lead to salvation. Yet the growing plant must be hedged round to protect it until it has grown into a tree. The tender plant of spirituality will die if exposed too early to the action of a constant change of ideas and ideals. Many people, in the name of what may be called religious liberalism, may be seen feeding their idle curiosity with a continuous succession of different ideals. With them, hearing new things grows into a kind of disease, a sort of religious drink-mania. They want to hear new things just by way of getting a temporary nervous excitement, and when one such exciting influence has had its effect on them, they are ready for another. Religion is with these people a sort of intellectual opium-eating, and there it ends. “There is another sort of man”, says Bhagavan Ramakrishna, “who is like the pearl-oyster of the story. The pearl-oyster leaves its bed at the bottom of the sea, and comes up to the surface to catch the rain-water when the star Svâti is in the ascendant. It floats about on the surface of the sea with its shell wide open, until it has succeeded in catching a drop of the rain-water, and then it dives deep down to its sea-bed, and there rests until it has succeeded in fashioning a beautiful pearl out of that rain-drop.”
This is indeed the most poetical and forcible way in which the theory of Ishta-Nishtha has ever been put. This Eka-Nishtha or devotion to one ideal is absolutely necessary for the beginner in the practice of religious devotion. He must say with Hanuman in the Râmâyana, “Though I know that the Lord of Shri and the Lord of Jânaki are both manifestations of the same Supreme Being, yet my all in all is the lotus-eyed Râma.” Or, as was said by the sage Tulasidâsa, he must say, “Take the sweetness of all, sit with all, take the name of all, say yea, yea, but keep your seat firm.” Then, if the devotional aspirant is sincere, out of this little seed will come a gigantic tree like the Indian banyan, sending out branch after branch and root after root to all sides, till it covers the entire field of religion. Thus will the true devotee realise that He who was his own ideal in life is worshipped in all ideals by all sects, under all names, and through all forms.