One should not become egoistic, thinking that one is doing great service. Actually, service is meant to kill ego. You can not call it service if it is rendered with ego. First of all, ego has to be subdued. Body attachment is the root cause of ego. Ego will vanish once the body attachment is given up. The spirit of oneness will develop once the ego is annihilated.
(From : Sai Veda, The Word of God, sayings of Bhagawan Sri Sathya Sai Baba)