Sri Aurobindo
Letters of Sri Aurobindo
9. Fate and Free-Will, Karma and Heredity, etc
Sacrifice has a moral and psychological value always. This 
value is the same no matter what may be the cause for which the sacrifice is made, provided the one who makes it believes in the truth or justice or other worthiness of his cause. If one makes the sacrifice for a cause one knows to be wrong or unworthy, all depends on the motive and spirit of the sacrifice. Bhishma accepting death in a cause he knew to be unjust, obeyed the call of loyalty to what he felt to be his personal duty. Many have done that in the past, and the moral and psychic value of their act lies, irrespective of the nature of the cause, in the nobility of the motive.
As to the other question, in this sense of the word ‘sacrifice’, there is none for the man who gives up something which he does not value, except in so far as he undergoes loss, defies social ban or obloquy or otherwise pays a price for his liberation. I may say, however, that without being cold and unloving a man may be so seized by a spiritual call or the call of a great human cause that the family or other ties count for nothing beside it, and he leaves all joyfully, without a pang, to follow the summoning Voice.
In the spiritual sense, however, sacrifice has a different meaning – it does not so much indicate giving up what is held dear as an offering of oneself, one’s being, one’s mind, heart, will, body, life, actions to the Divine. It has the original sense of “making sacred” and is used as an equivalent of the word yajña. When the Gita speaks of the “sacrifice of knowledge”, it does not mean a giving up of anything, but a turning of the mind towards the Divine in the search for knowledge and an offering of oneself through it. It is in this sense, too, that one speaks of the offering or sacrifice of works. The Mother has written somewhere that the spiritual sacrifice is joyful and not painful in its nature. On the spiritual path, very commonly, if a seeker still feels the old ties and responsibilities strongly he is not asked to sever or leave them, but to let the call in him grow till all within is ready. Many, indeed, come away earlier because they feel that to cut loose is their only chance, and these have to go sometimes through a struggle. But the pain, the struggle, is not the essential character of this spiritual self-offering.