It is well-known that temples devoted to Brahma are extremely rare compared to temples devoted to Vishnu and Shiva (or, indeed, any number of other deities, e.g. Murugan, Ganesh, Hanuman, etc.).
Question 1: Why is this?
I am of course familiar with (what I assume is) the standard mythological justification - in one of the Puranas (not sure which), Brahma and Vishnu tried to race to the top of an infinite Shivalingam; Brahma lied about having made it to the top; he then incurred Shiva's wrath, and was thus cursed that he would never again be worshiped.
Question 2: Is that really all there is to it? I find it somewhat surprising that this solitary tale would suffice to prevent a "Brahmite" sect (so to speak) from ever arising.
"I am of course familiar with the standard mythological justification."
The story you mention isn't actually the standard justification for why Brahma isn't worshiped. But since you were wondering, the justification you give is from the Vidyeshwara Samhita of the Shiva Purana. In this account, Brahma and Vishnu argue about who is superior until this argument turns into a battle. The battle threatens to destroy the three worlds, so the devas (gods) go to Shiva for help. To stop the conflict, Shiva turns into a pillar of fire that seems to go forever in both directions. Both Brahma and Vishnu are curious about what it is, so Brahma turns into a swan to go to the top, and Vishnu turns into a boar to go to the bottom. Both are unsuccessful, but Brahma lies that he went to the top, presenting a Ketaki flower that arose from the middle of the pillar and claiming it's from the top. Vishnu concedes defeat, but then Shiva appears, Vishnu touches Shiva's feet and as a result Shiva grants Vishnu the privilege to be worshiped as an equal to Shiva. Shiva then creates the demon Kala Bhairava to cut off Brahma's fifth head, but Vishnu persuades Shiva to take mercy on Brahma, so Shiva instead curses Brahma that he can't be worshiped in temples.
The version of the story given in the Shiva Purana is likely a later interpolation, because it differs from more common versions in a variety of ways:
In most versions the argument between Brahma and Vishnu does not come to blows;
In most versions Shiva explicitly offers help to the two gods by proposing a race;
In some versions Shiva just turns really tall without turning into fire;
In most versions the Ketaki flower falls from Devaloka instead of the middle of the pillar;
In Vaishnava versions Vishnu just touches Shiva's feet to tickle him so he'll bend down and Vishnu can touch his head and win.
But the most important difference for our purposes is that in most versions, Kala Bhairava actually does cut off Brahma's fifth head rather than showing mercy, and Shiva does not actually put any curse on Brahma. (In fact in these versions the opposite happens: Brahma puts a curse on Kala Bhairava that he'll be a vagabond.)
In any case, the more common justification for why Brahma isn't worshiped actually comes from another story, one recounted in many places, for instance in this excerpt from the Uttara Kanda of the Padma Purana. (I described it earlier in this answer.) A group of sages were conducting a yagna (ritual) on the banks of the Saraswati river, when they started to wonder (on the prompting of Narada) which god to dedicate the ritual to. So they sent sage Bhrigu (famous for his short temper) to test which god out of Brahma, Vishnu, and Shiva was most worthy. When he went to see Brahma, he put his hands together to salute Brahma. But Brahma was too proud to honor Brighu in any way, so outraged by this disrespect Brighu cursed Brahma that he would no longer be allowed to be worshiped. (By the way, if you're interested Vishnu was the one who ultimately won the test, although it had major ramifications that led to the story of Tirupati Balaji, AKA Venkateshwara.)
Everyone here has given the answers based on mythology.
Mythological stories were a tool to mainly teach people to either avoid certain behaviour and / or to aspire and strive to improve one's self by adopting desirable traits. To the intelligent, it should thus be self-evident that they are not meant for literal interpretation.
Brahman: The GOD (a very simple interpretation).
Brahmin: A student of the vedas who leads a dharmic life; scholar.
Brahma: God of creation (the creator; part of the trinity).
The Puranas describe the creator Brahma as the manifestation that Brahman assumes for the purpose of any creation. Brahma, thus having the nature of Brahman, is considered as the veda incarnate and the embodiment of knowledge.
Worship in Hinduism is steeped with symbolism. Very briefly -
Whether it is the vedic form or the agamic form of worship, both heavily utilise symbolism to reinforce a concept of what the deity being worshipped represents and / or the focus of the worship. Symbolism is used to reinforce religious teaching to increase ones understanding about some concept or the deity being worshipped, thus increasing our spiritual wisdom.
For example, the vedic form of worship do not utilise idols or shrines and is offered in the form of yagnas, almost always with a ritual fire. Oblations are offered into the fire, along with vedic chantings. As we place the ahuti (offerings) into the flame, we symbolically offer all our "impurities" - our anger, greed, jealousy, grudges, pains, obstacles - and pray to God to make us as pure as the offerings we give to Agni. Performing a Yagna itself is a symbolism of the unity of the physical (e.g. the heat from the fire) and meta-physical (e.g. the Vedic mantras), to achieve desired physical, psychological and spiritual benefits.
Now, the agamic form of worship is based on idols and temples, along with other associated rituals. The agamic scriptures have many parts out of which the Kriya pada of each Agama describes in detail the rules for constructing a temple or sculpting a diety (among many other things). And these rules have either a sound reason and / or is symbolic to specify something. For example, the mudras (gestures) of an idol that has fingers pointing down symbolize that the God is of a charitable nature, where as the mudra where the fingers point upwards (as in blessing someone) signify a protector.
Since we are talking about temples (whether of Brahma or Vishnu or anyone else), we are essentially talking about the agamic form of worship in Hinduism.
As mentioned earlier, the agamic scriptures deal with the philosophy and spiritual knowledge of worship of a deity. Every idol or form that is used for such worship is different because each symbolically represent the different characterisation of the deity being worshipped, based on the philosophy that the scriptures define about said deity.
As the scriptures (and existence of temple) point out, it isn't as if Brahma isn't / wasn't worshipped at all. The Garbhadhana (conception ritual), Punswana (fertilization ritual), Chudakarma or Keshanta karma (ceremonious tonsuring), Vivaha (wedding ritual) are all also associated with Lord Brahma. There are also funeral rites where Lord Brahma is invoked. All these can be symbolically considered as the act of creation or new beginning. Thus, logically, you would turn to the Creator to please / appease him.
But then, you can also turn to Vishnu, the protector, or Shiva the destroyer to please or appease them, for these very things. Why not offer worship to any one or any two or all of them? Such perceptions lower the importance of Brahma in the eyes of the followers of either Vishnu or Shiva, and would have certainly contributed to his loss of followers.
Brahma is also represented symbolically as the veda itself - the reservoir of all knowledge. (In this context, a cosmic power of the ultimate reality - the knowledge that contains the knowledge of all the phenomena evolved from it. Or in simpler words TRUE KNOWLEDGE.)
Worship is based on faith. And to faithfully believe something means you do not question it. Yet, the quest for knowledge starts with doubts, questions, debates and discussions. Thus, a faith based worship of Brahma - the manifestation of true knowledge - is a philosophical contradiction, as faith is often an hindrance to anyone on the quest of knowledge.
Thus, the REAL reason that ancient scholars didn't "worship" Brahma is to resolve such philosophical contradiction that his role as the creator and his primacy as the source of all knowledge created.
The quest for knowledge is itself a desire and an act of veneration of "knowledge" (as a deity). Thus, studying and following the vedas can by itself be considered as a worship of Brahma, and what all Brahmins do. And the evolution of our scriptures is a testament to this - an indirect reference to the importance (and equality) of Lord Brahma within the trinity, by the ancient scholars.
(Our philosophy has stood the test of time because it is based on sound reasoning - not because of what some God did to another God or somebody blessed or cursed someone. Such literal interpretation can really inhibit our spiritual growth.)
(For the spiritually inclined -
This also reminds me of the the approach of ancient Islamic scholars on how to teach their religion. When the young muslims were introduced to their religion, they were taught that "Doubt" is haram (forbidden; something to be avoided; a sin even if done with good intentions).
The reasoning was that due to the limitation of a child's understanding, more emphasis was placed on faith (which can also be described as absence of doubt). But as they become older they were urged to explore more - as prophet Muhammed (pbuh) did in long meditations resulting in the revelation of the holy Quran to him by God.)
The puranas are the stories of the worshipers(bhakta in sanskrit) and are far from truth. Brahma was a non-prominent deity, was worshiped in rigvedic period by means of a few sukthas only. Early rigvedic period had one set of deities while the fag end, i.e., in mandalas 1 & 10, one will find another set. worshipers changed deities many times and the sage Sankaracharya brought five more dieties, namely Rudra(Siva), Vishsnu, Lakshmi, Parvati, Ganesha who are the prominent deities now even.
In the Hindu Trinity of Brahma-Vishnu-Shiva, Lord Brahma is the Creator of the Universe and all living beings are said to have evolved from him. Brahma is also believed to have created the Saptarishi, or seven great sages, to help him create the Universe.
When Brahma creates the world, it remains in existence for 1 of his days, which means 2,160,000,000 years in terms of Hindu calendar. The world is said to exist for one Kalpa, or one day in the life of Brahma. Brahma is then believed to go to sleep for one night, which is as long as a Kalpa. When Brahma goes to sleep at the end of his day, the world perishes in fire. When HE awakens, HE again restores the whole creation.
This process (Pralaya) goes on till 100 years of Brahma's life is completed, which is the life span of Brahma. When this period ends, HE himself loses his existence, and HE and all Gods and Sages, and the whole universe get dissolved into their constituent elements. And this whole process of creation and destruction repeats itself ceaselessly, the world getting re-created endlessly...
Inspite of the above immense role, Why only three Temples of Brahma in the World?
Legend has it that Lord Brahma is said to be very liberal with granting boons and is easily pleased when prayed to without any thought as to who is praying and asking him for a boon. HE is rather callous in granting boons to the demons unguardedly.
All the deadly demons, from Hiranyakashipu to Ravana, received their boons from Brahma, which made them singularly notorious in destroying the noble virtues of the world. Then it became necessary for Lord Vishnu to appear in his various reincarnations to kill these demons.
That is why the cult of Brahma's worship declined as HE became unpopular amongst religious devotees who began to deem Brahma as the sole God of worship for the demons. Another reason why Brahma is not widely worshipped is the belief that being the Creator, his work is complete, at least for the time being.
Hence, there are innumerable temples of Lord Vishnu and Lord Shiva around the world, while Lord Brahma has only 3 temples, all in India, one at Pushkar Lake in Ajmer, another in Khokhan - Kullu Valley and the other at Khedabrahma in Kerala.
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