Athithi Devo Bavo (guests are equivalent to god).

Living is a continuous process of cell generation and cell decay. When any one of these stop, it is not healthy anymore.

When the cell generation impedes, it is decomposition.
When the cell decay impedes, it is cancer.

When a cell decay, replenishes the cells in other beings, this is called creation.

A musician burns few cells and creates pleasant tones. When a receptive person is pleased with this music, his/her cell lifetime increases 2x to 10x. As mentioned by one of the wise sages, Tirumular, extending the lifetime of a single cell, is equivalent to saving a life. Demise of a single cell with unpleasantness is equivalent to killing a life.

There is also an uncommon phenomenon where both cell generation and decay stops. In east, it is called as Jeeva samadhi (self-preserved being). Yoganandha's body exhibited this phenomenon in Los Angeles (USA), but this is quite common in himalayas and several hills in south india.

The purpose of the Pūjā (ceremonies) is to direct the energies towards creation. Rituals are devised to accomplish this by blocking certain virtues in people, referred as shatripus (6 virtues). This is not just a philosophical innuendo. Physically, the cells in the body decay at faster pace when the breath rate increases. All of these virtues demand increased oxygen and faster blood flow, killing a lot more cells without any physical exhaustion.

Godliness is being devoid of these six menial obstacles (shatripus);
1. Kama(m)  - Desire ( often referred to lust, but also includes desire for wealth and fame)
2. Krodha(m) - Wrath (outbursts of anger, destruction)
3. Lobha(m) - Greed (resulting in hoarding, manipulating resources, over-consumption)
4. Moha(m) - Delusion (resulting in traits like attachment)
5. Mada(m) - Arrogance (resulting in traits like pride)
6. Matsarya(m) - Cunningness (resulting in traits like envy)

This is similar to seven-sins discussed in western countries, except that they branch out the Lobha (Greed) and call Gluttony as yet another sin.

One can get rid of these in themselves with self-realization and effort (sadhana). But there is no direct way to impart it on others. Pleasing the five outward senses is an attempt to trigger the godliness in them.

1.) Fragnance (Dhupam): Incense sticks are lighted to ensure the sense  of smell is pleased. When the pleasant smell from a naturally occurring substance is spread, it makes the person either meditative or compassionate, based on their nature. In general, this bereaves Kama (desire, மண்-பொன்-பெண்-புகழ் ஆசை). In yogic terms, it pleases the moladhara and swadistana chakras.

2.) Food (Naivedyam):  The sense of taste is pleased with good food. Sattvic food is served, which predominantly wanes the Lobha (Greed) nature of a person. Manipura chakra is pleased.

3.) Dress Code (Vastram): We adopt a certain dress code naturally, this is to obtain the right sense of touch. Materials that are still close to nature like cotton, wool, silk that are neither over-processed nor synthesized,  diminishes the Moha (Delusion) nature in a person. Anahata chakra is pleased here.

Often a lot of fragrant flowers are used to please the sense of sight, smell and touch.

4.) Portraits and Statues (Vigraham): The portraits and statues of gods are depicted as accomplished and super evolved beings to please our sense of sight and at the same time it destroys the Mada (Arrogance) in us. The songs, stories and enactment on the extraordinary achievements (parakramas) of divine beings are exhibited to constantly keep a check on our arrogance.  This relates to Vishudhu chakra.

5.) Music (Mantram): Incantations, certain musical instruments and vocals are to please sense of hearing and at the same time dissolve the Matsarya (Cunningness) nature in us. Matsarya is the result of the mind, mantras are life-forming sound energies, which are repeated to bore the mind to stillness. Agna Chakra is the immediate benefactor of this.

Krodha (Wrath) needs all these 5 senses to be in pleased state to stay dormant. When any one sense is disturbed, it erupts.

When all these 6 virtues are dissolved, it is called the dissolution of ego. This is not a permanent attainment, but an experience like joy, sorrow, fear and anger. Everyone can get the glimpse of it, get to experience it in momentary lapses. The wiser ones keep extending the duration of the experience every time. When someone is undergoing this experience, they are in par with what is commonly perceived as god.

Call it celebration, get-together, party, wedding, baby shower, house warming, ceremonies, ritual, Pūjā and also going to religious places of worship, all this is done to defer these shatripus in us. If the ritual successfully deter these obstacles, it is the rise of godliness, at least for that time being, and the verse Athithi Devo Bavo is indeed a prophecy fulfilled.