Thirumanjanam is similar to Abhishkam, and it is a kind of seva, and it would be performed in most of the Vishnu Temples. Before performing Thirumanjanam to Lord Vishnu and Mata Lakshmi, the idols would be cleaned with oil, turmeric and sandal paste. Then if Thirumanjanam (Abhiskhekam) is performed to the deities, the items used for Thirumanjanam like milk, coconut water and honey would become purified, and it would be distributed amongst the devotees. By consuming the holy Prasad items, the devotees would get relieved from the bodily related ailments, and their life would prosper.
The Madhwa saints, Vaishnavites and the Alwar saints have treated Lord Vishnu as a childand wrote lot of bhakti poems on Lord Vishnu, and sung in front of the temples. Bathing of the holy idols (Thirumanjanam) is considered as a very sacred act by the Alwars, and they have done it with sincerity and dedication.
There are various ways to express our bhakti, and one such method is doing Thirumanjanam in the temples. Thirumanjanam seva can be done by the devotees in famous Vishnu temples by paying the prescribed amount to the temple office.
During the period of Sri Ramanuja, he used to sincerely do Thirumanjanam to the deities at the Srirangam Temple, and used take his food only after doing that. Due to that, during his period, people who lived in Srirangam lived a blessed life, and they didn’t suffer from big problems in their life.
Sri Ramanuja and his disciples used to give the Thirumanjanam Prasad to the devotees, and after consuming it, the bad minded people had become pious and holy, and it was mentioned in the life history of Sri Ramanuja itself.
The almighty is regularly showering his grace on us, and gives us a good life, and hence, we have to offer our sincere prayers to him, perform puja and Thirumanjanam / Abhishekham to him, in order to get all kinds of prosperity in our life.