The Rigveda starts with the word Agni or fire. It is from the fire all creatures are generated and when the fire goes from our body we die. The Vedic religion is basically a religion of fire worshippers. They worshipped fire because worshipping earth may take you aeons, because the chief character of earth is stability. Worship of water is unwise because water is the main substance, which makes up the body and most of us identify too strongly with our body. Worship of air is likely to make you seriously unstable. Since fire is the representative of the sun on earth and without sun life cannot exist on earth, fire is worshipped. The fire also purifies and amplifies whatever is offered to it. The worship of fire is meant to purify the fire element in the body and to purify the consciousness by amplifying the Mantras we repeat. The Vedic worship of fire is known as Yajna, which is extremely detailed and complicated.