Why do you think we give God an offering? Do you know from where this belief emerged? You must have noticed that Hindus give God a plateful of offering. People sometimes even go up to the extent of making sacrifices to God though that has been made illegal by the government a long time ago . Let us see that from where this custom of giving God an offering or 'prasad' of fruits and several other things came into being.
Early Days- Since the time man was a primitive being, he feared all the forces of nature. A heavy rain or lightening frightened him. He thought that some unseen force is sitting high in the sky and wrecking havoc in their lives for some unknown reason. They were frightened when all their crops got destroyed due to some natural calamity like storm, fire or rain.
So, they started giving a part of their produce or food to 'God' or the unknown power as an offering. They wanted to please the unknown and unseen forces in heaven. First they started with fruits and vegetables and then they started sacrificing animals in the honour of God. This practice came down the ages to form the popular Hindu belief that, you have to give God an offering or 'prasad' in the form of fruits, vegetables or meat whenever there is a religious festival or an event.
As A Bribe- Most of the times we remember God only when we are in deep trouble or wish for something. Any time we fall in a situation from where it is difficult to come out, we take the name of God. And we do it even when we need good marks in examination, promotion, familial happiness or wish to have lots of money and luck. So, we think that if we give an offering to God he will be pleased and will grant all our wishes. But the fact is God helps those who help themselves. Both hard work and luck go hand in hand with each other.
As A Thanks Giving- We keep on believing and following things blindly without trying to validate the cause behind them. Some give an offering to God just because this is an age old custom and others do it because they believe this is a small token of thanks and acknowledgement for whatever God has given them. Actually this is the best logic for giving 'offerings' to God, as we often forget to thank God after we get what we want. So take out some time everyday and thank God for whatever He has given to you.
Try to understand the root cause behind this Hindu belief of giving God an offering before you blindly follow the custom.