What is the philosophy of animal sacrifice? Can we spend in charity instead?
Before I answer your question let me first point out that animal sacrifice is an optional worship ritual on 'īd. It is not mandatory; however, it is highly desirable if its underlying philosophy and wisdom is understood.
Now coming to this philosophy:
There are many things which must not be taken on their face value; they have a deeper significance and philosophy. They symbolize certain realities and are not an end in themselves. For example, a country's flag symbolizes its national entity and honour. The piece of cloth in itself is nothing if we come to think of it; however, if we view it as a representative of our solidarity and honour, we may become so emotional about it that our patriotism will not let us drop it to the ground. We would even lay down our lives for it. The second thing that perhaps needs to be considered is that once a country's flag is invested with such significance, no other act or practice can replace it or replace our sentiments for it. Thus for example we cannot say that a country's national anthem can replace its flag – both have their own independent significance.
Animal sacrifice is also a symbolic act. It is not an end in itself as the prayer or the zakah for example are. It is a means to an end. We must discover the end.
The reason for animal sacrifice on eid is to commemorate a great event which depicts an extraordinary expression of submission to the command of Allah – the essence of Islam. The Prophet Abraham (sws) while obeying the Almighty set a platinum example of this submission. When we offer an animal in sacrifice, we actually symbolize our intention that we are ready to sacrifice our lives for the cause of God whenever the need arises.
Another conclusion that can be drawn is that no other act of worship can replace animal sacrifice since animal sacrifice has a specific significance. It is much like saying that hajj and zakah are not interchangeable since both have their own purpose and importance.
Actually an important thing which hinders our understanding of animal sacrifice is that we think that its primary purpose is to feed the poor and hence the question instantaneously comes to our mind as to why we cannot help the poor in some other more productive way like, for example, providing them with vocational training or sending the younger lot to school. Now what needs to be realized is that feeding the poor is a secondary purpose of animal sacrifice. Its primary purpose as explained above is to symbolize the fact that today we are presenting this animal for sacrifice to God -- tomorrow if a need arises, we will present our life too for the cause of God. So it is primarily this symbolism which must always be looked at when understanding the act of animal sacrifice and not feeding of the poor with the slaughtered animal's meet. Moreover, it is to this reality that the following verse points:
لَن يَنَالَ اللَّهَ لُحُومُهَا وَلَا دِمَاؤُهَا وَلَكِن يَنَالُهُ التَّقْوَى مِنكُمْ كَذَلِكَ سَخَّرَهَا لَكُمْ لِتُكَبِّرُوا اللَّهَ عَلَى مَا هَدَاكُمْ وَبَشِّرِ الْمُحْسِنِينَ (37:22
The flesh and blood [of] these [sacrificed animals] does not reach God; it is only your piety that reaches Him. Thus has He subjected them to your service so that you may give glory to God for guiding you. [This is the way of the righteous] and [O Prophet!] give glad tidings to these righteous. (22:37)
Thus, while helping the poor in various ways is itself a very commendable practice, yet it cannot take the place of animal sacrifice.