To understand the concept of pouring milk over Shiva Lingam, we must understand the concepts of Rudra and Shiva.
When all forces are in equilibrium, everything is in equilibrium– hence there is no reaction. It can be called singularity (स्थिति). At that stage, there is no space (देश - sequential interval of objects) or time (काल - sequential interval of events) or sequential coordinates (दिक् or position) concept, because everything is perceived through time-evolution of boumd particles in space and time that require energy (रजसा उद्घाटितम्). The biggest (बृहिँ वृद्धौ॑) such singularity (स्थिति) that comes into perceptual existence (ब्रू॒ञ् व्य॑क्तायां वा॒चि) through breaking of the equilibrium (बृहूँ उ॒द्यम॑ने) generating longitudinal waves (बृहिँ शब्दे॑), holds (डुभृ॒ञ् धारणपोष॒णयोः॑) and covers (भृ॒ञ् भर॑णे) everything in a region, is called Brahma (ब्रह्मा).
When the equilibrium is disturbed, it leads to two equal and opposite reactions – one moving out from the central point called Gati (गति) and the other trying to confine this outgoing energy and known as Agati (आगति). The first such reaction (गति) was what is now known as the big bang. It changed from a static imperceptible singularity to express everything (रूपं रूपं प्रतिरूपो बभूव तदस्य रूपं प्रतिचक्षणाय । इन्द्रो मायाभिः पुरुरूप ईयते युक्ता ह्यस्य हरयः शता दशेति ॥ ऋग्वेदः 6-47-18) by release of energy, which spread out everywhere, got slowed down due to the resistance of the background field due to a bow shock effect and came to a halt cutting of a measurable volume called the Universe. For this reason, the confining force (आगति) is called Maya (मा॒ङ् माने॑). This is the mother force, which pervades everything and leads to all other forces that balance each other to stabilize the universe. The confining and all pervading force (आगति) is known as Vishnu (वि॒षॢँ॑ व्या॑प्तौ).
The central outgoing disturbance to the equilibrium (गति) made everything perceptible (स जातो भूतान्यभिव्यैख्यत्किमिहान्यं वावदिषदिति । स एतमेव पुरुषं ब्रह्म ततममपश्यदिदमदर्शमिती३ ॥). Since it was like fuel (ञिऽइ॒न्धीँ दीप्तौ॑) for everything (तस्मादिदन्द्रो नामेदन्द्रो ह वै नाम तमिदन्द्रं सन्तमिन्द्र इत्याचक्षते परोक्षेण), it is called Indra (स योऽयं मध्ये प्राणः । एष ऽएवेन्द्रस्तानेष प्राणान्मध्यत ऽइन्द्रियेणैन्द्ध यदैन्द्ध तस्मादिन्द्धऽ - शतपथब्राह्मणम् -6-1-1-2).
Pure outward motion (गति) is called Indra. Pure confining motion (आगति) is called Vishnu. There is continuous interaction between these two forces (इन्द्रश्च विष्णो यदपस्पृधेथां - ऋग्वेदः 6-69-8) in a balanced manner (उभाजिग्यर्थुन परा जयेथे - तत्रैव). By themselves, they are not perceptible. But when they move through a point in equilibrium, outward motion (गति) is called Indra becomes Agni (अग्निम्), because that only leads to creation of form – hence ultimately, it is called fermions. The confining motion (आगति) called Vishnu, becomes Soma (सोम), because it confines the fermions to give it a shape – hence create objects (षु॒ प्रसवैश्व॒र्ययोः॑).
When Indra and Agni combine, it has the potential for destroying everything. Hence, it is called Rudra (रु॒ङ् गतिरोष॒णयोः॑). For reasons not being discussed here, it has 11 divisions with specific functions. When Vishnu and Some combine, it becomes Chandra (चदिँ आह्ला॒दे दीप्तौ॑ च). When Rudra becomes Chandrasekhara (confined by Chandra), He becomes Shiva. The seasonal plants are influenced by Sun’s rays. The perennial trees are influenced by Moon’s exosphere and grow at night. Hence, during auspicious days, fruits of perennial trees like coconut, jackfruit, mango, amla, etc., only are prescribed and those of seasonal plants like rice, wheet, etc., are prohibited.
Simply putting up a lingam in some place does not make it a Deity or give desired results. To invoke the powers of Shiva, it is necessary to have Prana Pratishtha, which is a highly technical process. It requires the knowledge of the elements through a separate branch of science (वर्णौषधि विज्ञानम्) to decipher the Mantra after first determining it (मन्त्रोद्धार) through another technical process. Simply citing the Mantra will not help.
Shiva is basically Rudra confined. There is every possibility of Rudra coming out of the confinement and destroying everything. Hence, it is necessary to keep the guard to avoid mishap. For this reason, it is recommended to fill it with the elixir of life – Milk (दुः॒अँ॑ प्र॒पूर॑णे). But it is effective only in old temples established in Vedic ways. Pouring milk on roadside temples is a sheer wastage of milk.
An Article by Sri Basudeba Mishra
(Readers can follow him on his facebook page and read his wonderful writeups.)