Regarding the questions you asked: self has really two meanings, or is used in two senses, in the Bahá'í writings; one is self, the identity of the individual created by God. This is the self mentioned in such passages as "he hath known God who hath known himself", etc. The other self is the ego, the dark, animalistic heritage each one of us has, the lower nature that can develop into a monster of selfishness, brutality, lust and so on. It is this self we must struggle against, or this side of our natures, in order to strengthen and free the spirit within us and help it to attain perfection.
Self-sacrifice means to subordinate this lower nature and its desires to the more godly and noble side of our selves. Ultimately, in its highest sense, self-sacrifice means to give our will and our all to God to do with as He pleases. Then He purifies and glorifies our true self until it becomes a shining and wonderful reality.
- Shoghi Effendi (From a letter dated 10 December 1947 written on behalf of Shoghi Effendi to an individual believer; The Compilation of Compilations, vol. II, Living the Life)