All religious traditions have one purpose, to elevate man by freeing him from his cares and worries. A human being has worries that are not shared by other creatures. But it must be noted that all religious systems proclaim that man can not only free himself from his cares, if he makes an effort, but that he can also attain the enlightenment that is not within the reach of other creatures. They speak in one voice that he will be rid of his cares if he goes for refuge to the Great Power that rules all worldly activities. Devotion or bhakti is a feature common to all religious schools- Advaita (non-dualism), Dvaita (dualism), Visistadvaita (qualified non-dualism), Saiva Siddhanta, Christianity, Islam and so on. The Buddha did not speak of devotion but it seems his followers cannot regard their master without bhakti. They have deified the Buddha and created images of him that are bigger than those sculpted for any deity. In very recent times a number of jnanins have laid stress on inquiry into the Self as the sole means of liberation. But they are themselves worshipped as God by their followers. Bhakti is an inborn characteristic of man; it is indeed an organic part of him.
Devotion in the Advaita system implies adopting an attitude of non- difference between the worshipper and the worshipped; that is the devotee must look upon Isvara as not being different from himself. It might be asked: "The devotee who worships the omnipotent and omniscient Lord has only very limited strength and knowledge. How can the two of them be the same? " But the question also arises: "Does God regard us as being different from himself? If there are objects, entities, different from God how did they originate? If they came into existence as entities separate from Him how can He hold sway over them? ".
If we think on these lines it will become clear that the one and only Paramatman exists in various forms: if the ocean stands for Isvara we have in contrast the pond, the well and the little quantity of water contained in a spoon and soon that stand for diverse living beings. The water in all is the same. There maybe differences in the strengths of the various entities. But if you go to the base, the ground or root, you will discover that they are the same. If we go to the root we will become one with the root. This is liberation according to Advaita. Merely to talk about non-dualistic liberation is nothing more than an Intellectual exercise and will serve no purpose. The truth of such liberation must become an inward reality. In other words the quest must culminate in actual experience and it can be had only with the grace of Isvara. Great sages proclaim that it is only with the blessings of that Power which keeps us in a constant whirl of action that the whirl will stop and that we will have the Advaitic urge to seek the ground. "Isvaranugrahadeva pumsam Advaitavasana. "
Even in the initial stages when we feel that Isvara and his devotee are separate, we must try to cultivate the awareness, albeit to a small degree, that the Paramatman who appears as Isvara is the same as the Paramatman that has become "us". If such be our approach, our love for the Lord will become more intense. After all, is there anything or anyone we love more than ourselves?
Isvara awards us the fruits of our actions. If we become more and more devoted to him, as recipients of his grace, we will get closer and closer to him. He will himself reveal to us who he is and there will be no need for us to inquire about him or into him. In response to our devotion he will deign to reveal his true nature to us. He declares so in the Gita: "Bhaktya mam abhijanati yavan yascasmi. . . . " (By devotion he comes to know who in truth I am. . . ).
Countless are the attributes of Isvara that bespeak his surpassing beauty and auspicious qualities. Devotees find constant delight in contemplating them. But for the jnanin, the enlightened one, the ideal is the Godhead that has no attributes and it is in his Godhead that he is finally absorbed. Sagunopasana (worship of Isvara with attributes) is the first step towards this end. For it our religion has evolved the concept of "istadevata" ("the deity of one's choice", "the deity one likes").
What is special about sanatana dharma or Hinduism as it has come to be called? Alone among all religions it reveals the one and only Godhead in many different divine forms, with manifold aspects. The devotee worships the Lord in a form suited to his mental make-up and is thus helped to come closer to the Lord with his love and devotion. These different forms are not the creation of anyone's imagination. The Paramatman has revealed himself in these forms to great men and they have had close contact, so to speak, with the deities so revealed. They have also shown us how we too may come face to face with these divinities, given us the mantras to accomplish this and also prescribed the manner in which the divine forms, whose vision they have had, are to be adored.
Bhakti or devotion is common to all religions whatever the manner of worship they teach. It is not exclusive to our faith in which different deities are reverenced.
For a general background, please see here