Bhagavad Gita

ದೇವಾನ್ ಭಾವಯತಾನೇನ ತೇ ದೇವಾ ಭಾವಯಂತು ವಃ ।
ಪರಸ್ಪರಂ ಭಾವಯಂತಃ ಶ್ರೇಯಃ ಪರಮವಾಪ್ಸ್ಯಥ॥೧೧॥
devān bhāvayatānena te devā bhāvayaṃtu vaḥ |
parasparaṃ bhāvayaṃtaḥ śreyaḥ paramavāpsyatha||11||

Gist of the sloka:
With the performance of the yagna, you would nourish the demi-Gods [devatas] and they in turn would nourish you. Helping each other, to obtain bliss.
Brahma after creation, directed the humankind, to perform yagna, to nourish the demi-Gods who would then bless the mankind of their desires. Thereby, completing the cycle and enriching each other.
It is a sense of false imagination, that we believe we can do and obtain things ourselves. Rather what we do is just plant the seeds and water it. Prakruthi [nature] with the guidance of the Lord determines which seed germinates and how. Lord does his miracles through the demi-Gods in many ways. Behind all is the force of Lord.
Behind every organ of our body, is a force of demi-Gods [who in turn are guided by Lord]. Without their grace and benevolence, we are incapable of anything. Lord has given us many organs like eyes, ears, tongue etc., all with the intention that we utilize them to seek good hear good and speak good. The good here being that which helps us to, elevate our souls – or the right knowledge about Lord. All of these are happening because of the presence of the demi-Gods and their benevolence. We should therefore be grateful to these demi-Gods who are members of the Lord’s family. We, by praying to them show our respect and they in turn bless us.
We generally consider worship through fire [fire sacrifice] as yagna. The reason being fire is the most pure, sacred visible and accessible object to mankind. All others like water, earth is in some form or fashion have some impurities. Fire has none. No matter what is put into it, it purifies it and reduces it to ash. If we dream of seeing something being actually taken in by the Lord, fire is the means for it. Fire is also the direct representation of the Lord. Lord himself is like a bright spark of light of knowledge. Fire represents such Lord. Worship of the fire within him is Agni Narayana, is yagna. Without this concept in our mind, we are only breathing in smoke and is a worthless effort.
Offering to the Agni Narayana reaches Surya Narayana [Lord within Sun]. The sun thereon provides the sustaining energy to the world. The reason the yagna is done in the daytime is to ensure the 7 [VIBGYOR] bright lights from the yagna fire matches the 7 bright lights of the sun.