Why do we offer food to the Lord before eating it?

Hindus make an offering of food to the Lord and later partake of it as prasaada – a holy gift from the Lord. In our daily ritualistic worship (pooja) too we offer food to the Lord.

The Lord is omnipotent and omniscient. Man is a part, while the Lord is the totality. All that we do is by His strength and knowledge alone. Hence what we receive in life as a result of our actions is really His alone. We acknowledge this through the act of offering food to Him. This is exemplified by the words “I offer what is Yours to You”. Thereafter it is akin to His gift to us, graced by His divine touch.

Basically there are two reasons why the food is offered to the Lord. One reason is that it is a way to serve the Lord and develop devotion (bhakti) for Him. But this reason presupposes that we ourselves have to prepare the food with a sense of devotion and commitment to God. The idea is that we actually prepare food for His pleasure, that He enjoys as someone we serve. Then after that we offer Him food, He accepts it and left the remains after a meal called prasada or literally “mercy”. In fact, He will not accept food in a physical form, but what He will accept is our dedication and devotion to Him. As I said, this is the case when we ourselves prepare the food with a sense of devotion and commitment to God.
You can offer food to the Deity (murti), or to the picture of the Lord or even without it, you can imagine in your mind the form of the Lord. Then you can offer food with folded palms saying the mantra. What mantra to pronounce? Vaishnavas pronounce some Vaishnava mantra. Shaiva devotees can pronounce some Shaiva mantra. Folded palms is a gesture of offering obeisances to the Lord. Then leave the Lord alone for a few minutes.
You should not think that the Lord is dead statue to which you are making offering. He is a living person, conscious person, the Supreme Person, the creator of the world, etc. He is all-powerful and all-pervading person, The Lord who can manifest Himself in front of us through the form of the Deity (murti), or the picture, or even through the form of the Lord we envisioned within the mind.

However if we offer food that we did not prepared then there is another reason why it is good to offer food to God.
It is said in Bhagavad-gītā 3.13 “The devotees of the Lord are released from all kinds of sins because they eat food which is offered first for sacrifice. Others, who prepare food for personal sense enjoyment, verily eat only sin.”
Produced food or food prepared by other people should be offered to the Lord in order to release the food of sin. I’ve heard advice that in this case we should just say “Shri Vishnu” three times. In this case food is not offered to the Deity (murti), ie not in front of Him as if He will eat.

Offering of food to the Lord is considered for a kind of sacrifice that frees from sin, but it can be much more than that. It can be a way to intimately associate with the Lord, a way to reciprocate the affection with Him, a way how to do something for Him.