The animal of sacrifice has been named shaeera (symbol) in the Quran (22:36). Mention is also made of the fact that neither its flesh nor its blood will ever reach God: it is human piety which will reach Him (22:37).
This shows that in Islam there are certain things which are significant as symbols and embody some inward reality. The animal of sacrifice is one of them. The word shaeera refers to a tangible symbol, indicative of some profound reality. For example, God requires His servants to sacrifice all un-Islamic feelings and ambitions. This is a psychological sacrifice. God has commanded people to sacrifice an animal as a symbol of that psychological sacrifice.
While making an animal sacrifice, a Muslim utters these words: ‘My prayers and my sacrifices, my life and my death, are all for God, lord of the Creation.’ His doing so expresses the idea that the sacrificing of an animal is no more than an outward symbol of an inward reality. A true sacrifice is when the slaughtered animal becomes a tangible symbol of having eliminated selfish desires and cravings.
The essence of fasting is to abstain from sinful actions.