According to Christian sources, idolatry is the worship of a Deity in a visible form. It can be a worship of either a symbolical representation of the one God or, of a ‘false’ divinity (www.biblegateway.com/resources/dictionaries). The Bible and the Quran provide the capital punishment to idolaters: stoning to death (Bible: Deuteronomy 17.2-5) and killing unless the idolater converts (Quran: Repentance 9.5). Although colonial Christians sometimes killed locals for such reasons, they are a bit more relaxed than Jews and Muslims about idolatry. Christians worship Jesus, who did take a visible form. Many revere certain icons, such as the shroud of Turin (believed to be the relic of Jesus’ resurrection). Catholic and Orthodox Christians use images in worship, which they call icons. The use of icons and relics is an old practice, early Christians used pieces of cloth touched by the apostle Paul for healing sick people (Bible, Acts 19.11-12).
We Hindus are sometimes not sure what to think of our Deity image worship (Murti puja). Most non-Hindus see us bow before Murtis, and simply conclude that we are idolaters. But we know in our hearts that it is not correct. Not just us, a few Christian scholars also thought it is probably better to not to make simplistic judgments about our Murti worship, they found it easier to claim it as something inherently deficient that Jesus came to fulfill (J. Farquhar: The crown of Hinduism). A few western Hindus became uncomfortable about the way this whole issue has been presented, and wrote easy reading books on the subject (Diana Eck: Darsan: seeing the Divine image in India). I do not know of any English work on this subject by an Indian Hindu that is worth reading.
What are we supposed to think? Let us explore that question.
Our spiritual goal is to see God or merge in God in this lifetime. Murti puja is a way to accomplish this goal. All Deities are the same one God. The Shvetashvetara Upanishad (4.1-2) says that the formless One Brahman used various powers to take multiple Deity forms, including Agni, Aditya, Vaayu, Chandra, Hiranyagarbha Brahmaa and Viraat Prajapati. They are only various aspects of Brahman. A famous verse of the Rigveda (1.164.46) also declares this message: “ekam sad vipraa bahudhaa vadanti, vayuryamogni maatarishvaan aahuh” (The one Sat Brahman is described in many Deity names, like Vaayu, Yama, Agni and Maatarishvaan). The Deities are paraspara-sambhuta (originated from each other). To take an example, in the Devisukta of the RigVeda, VagDevi Sarasvati is Divine Mother, origin of all, but in the Brahma-vaivarta Purana, She originated from Sri Krishna; in the Narada and Kurma Purana, She is the daughter of Lord Shiva; and in the Varaha Purana, She appeared from the combined vision of Lords Brahmaa, Vishnu and Shiva.
The Deities have multiple forms, as described in various mantras. It is said that they are the Divine Spirit of a mantra, “mantraatmikaa devataa” (Mimamsaa Darshan by sage Jaimini). Mantras also frequently describe the Deiform. Sage Shaunak wrote in Vrihad-devataa that to understand a mantra, we must know the Deity (1.2-4). However, Acharya Shankara said that a Deity can take any form (Brahma-Sutra 3.1.27).
How do Deity images help? The Brahma sutra (4.1.5) says, “Brahma-drishtih utkarshaat” [To exalt the image, it should be seen with the ‘everything and everybody is Brahman’-vision (but Brahman should not be seen as the image)]. Sages say that it is impossible for us to conceive of the vastness of God, and whatever we could imagine about God, would be deficient and flawed. Therefore, sages approved of images, expecting that it will help the common person to connect to God. We do not worship the image, but ask God to accept our worship through the image. It would be idolatry if this traps us to the Murtis. God in the Kapila incarnation said that Murti worship would be meaningless if the worshipper does not think of the transcendent God (Srimad Bhagavatam 3.29). We should not be too concerned, because by the grace of God, Murti worship does not trap us. To help us in this regard, sages have structured the worship for us. The story of saint Parashuram from a little-known village called Dhamrai in Bengal (1892 CE) should help explain the purpose of Murti worship. His story is found in the Sadguru-sanga by Sri Kuladananda Brahmachari. Parashuram was once a happy family man. When he became old, all his children died within a short time, and then his wife also died. After that, Parashuram decided to live the rest of his days in the Lord Krishna’s temple (Madhava temple) of his village. When other saints came to the area, he would go visit them. Once, saint Bijoykrishna Goswami was traveling through the region. Parashuram came to visit him. He asked Goswami prabhu for the blessing to see Madhava. To teach his own disciples, Goswami prabhu said to him, “You carry the image of Madhava in your sack, then why do you ask for this blessing?” Parashuram replied, “Oh no, not this Madhava, I want your blessing to see the Madhava who is inside this Madhava, the One who peeks out from time to time.”
Murti puja, is obviously not the only type of recommended worship. Lord Shiva teaches us how to conduct a purely Spiritual worship of Brahman with the seven-letter mantra “OM Sacchidekam Brahma” in the Mahanirvana Tantra (Ullaasa 1). It can only be a worship of the spiritually advanced, because it requires the Brahma-drishti.