The relevance of five elements in worship and pujas and other rituals is in their association with respective chakras. The chakras are subtle centers corresponding to spinal nerve centers in the body.
The earth element is associated with muladhara chakra (in
the lowest point of the spine at the end of the tailbone), of which Ganesha is
the presiding deity.
The water element is associated with the svadhisthana chakra
(at the level of the sex organs), of which Brahma (the creator) is the
presiding deity.
The fire element is associated with manipura chakra (at the level
of the navel), of which Vishnu (the preserver) is the presiding deity.
The air element is associated with the anahata chakra (at
the level of the heart) with presiding deity Shiva.
The akasha (space element) is associated with Vishuddhi
Chakra (at the throat level), with the jivashiva (Shiva in the individual) as
the presiding deity.
The sixth chakra, ajna (at the center of the brain, behind
the eyebrow-center), is the chakra of Guru.
Sahasrara, the seventh chakra, (at the crown of the head),
is that of Mahatripurasundari, the supreme Goddess. She may be substituted by
another Goddess or God.
These associations between elements and chakras are conceived
in order to invoke the powers of these deities for preparation of the ritual.
When one practices identification with a pure undiluted mind day after day, one
begins to realize the highest bliss closer and closer. Even when the highest
state has been reached, the practice is not to be abandoned, as a continuous renewal
or re-enactment of the act of creation is desirable for the good of the entire
universe.