The word pratika means “going towards”; and worshiping a pratika means worshiping, as a substitute, something which is, in one or more respects, like Brahman ब्रह्मन्, but is not Brahman. Along with the pratikas mentioned in Sruti there are various others to be found in the Puranas and the Tantras. In this kind of pratika, worship may be included all the various forms of pitri-worship पितृ -पूजा (ancestors-worship) and deva-worship.
Now, worshipping Isvara ईश्वर, and Him alone, is bhakti; the worship of anything else – deva or pitri or any other being-cannot be bhakti. The various kinds of worship of the various devas are all included in ritualistic karma, which gives to the worshipper only a particular result in the form of some celestial enjoyment, but can neither give rise to bhakti nor lead to mukti मुक्ति – liberation. One thing therefore has to be carefully borne in mind. If, as it may happen in some cases, the highly philosophic ideal, the Supreme Brahman, is dragged down by pratika-worship to the level of the pratika and the pratika itself is taken to be the Atman of the worshiper, his Antaryamin अन्तरयामि, then the worshiper becomes entirely misled; for no pratika can really be the Atman of the worshiper. But where Brahman Himself is the object of worship, and the pratika stands only as a substitute or a suggestion thereof, that is to say, where, through the pratika, the omni present Brahman is worshiped, the pratika itself being idealized into the cause of all, or Brahman-the worship is positively beneficial. Nay, it is absolutely necessary for all mankind until they have got beyond the primary or preparatory state of the mind with regard to worship.
When, therefore, any gods or other beings are worshiped in and for themselves, such worship is only ritualistic karma; and as a vidya, a science, it gives us only the fruit belonging to that particular vidya. But when the devas or any other beings are looked upon as Brahman and worshiped, the result obtained is the same as that obtained by the worshiping of Isvara.
This explains how in many cases, both in the Srutis and in the Smritis, a God or a sage or some other extraordinary being is taken up and lifted, as it were, out of his own nature and idealized into Brahman, and is then worshipped. Says the Advaitist, “Is not everything Brahman when the name and the form have been removed from it?” “Is not He, the Lord, the innermost Self of everyone?” says the Visishtadvaitist. “The fruition of even the worship of the Adityas, and so forth, Brahman Himself bestows, because He is the Ruler of all.” Says Sankara, in his Brahma Sutra Bhashya: “Here, in this way, Brahman becomes the object of worship, because He, as Brahman, is superimposed on the pratikas, just as Vishnu, and so forth, are superimposed upon images.”
The same ideas apply to the worship of the pratimas प्रतिमा – idol as to that of the pratikas. That is to say, if the image stands for a god or a saint, the worship does not result in bhakti and does not lead to liberation; but if it stands for the one God, the worship thereof will bring both bhakti and mukti.
Excerpts from: Vivekananda Yogas and Other Works