Thirumanjanam is Abishegam. Abishegam is a Tamil term with due reference to mainly saivaite formalities. Whereas the former is a term with reference to Vaishnavaites.
In our temples, our moolavars (presiding main sanctum deity) are made of karungkal, nava-pashana (9 poison/minerals) like the one of Lord Muruga in Palani Malai. If not they will be at least in Panch-lokha.
What is Pancha-lokha?
Pancha means five. It literally means 5 metals. This is a term that is used to describe a traditional five metal alloy comprising of gold, silver, brass, and iron with copper as the main constituent.
Back to Thirumanjanam
According to a blogger's father-in-law who explained to her the meaning behind Thirumanjanam, I summarised her lines.
These vigrahas are being applied with special preparations to ensure that the medicinal benefits are extracted from these vigrahas.
Before any kind of application of eatable items, the vigrahas are cleaned with oil, soap-nut, tumeric etc. These make sure cleanliness comes in place before abishegam items like yoghurt, honey,milk is applied to our deity. These are termed as eatable. When they are being applied, there is a transfer of a metallic flavour to the applied items. These items are then collected and distributed to devotees as prasadham.
The items now with a new flavour of energy, brings in additional strength, cleanses and clears any kind of in-built deficiencies. Hence Deiveega food is never comparable to normal food. There is a different energy level.
Thirumanjanam for Sri Lakshimi Narayana
Another concept is, these vigrahas are usually metal and stone statues. They are still material. These statues have to be cooled regularly in order to prevent expansion of solids which have the tendancy to deform or crack the structure. Thirumanjanam keeps the statues at optimal temperature.
Finally,
To the common man on the streets, he believes bathing God with such delicacies is to uphold his greatness and his high standing in the universe.
To the atheist, he believes we are people who waste food items over a statue. But the fact is, Hinduism is science. There is nothing right without the statutory of science involved.
To a devotee, bathing God and adorning him with vaastram, jewellery is like treating him like our child with love.