Sri Agni is the adhidevata of the Sun and is the most revered deity of the agnihotri’s and brahmins of the vedic period. He has two wives named ‘Svaha’ and ‘Svadha’ who carry the offerings made by the devotees into the holoy fire (Agni devata) to the Gods and manes respectively. The three lokas are worshipped with the bija mantras ” OM bhu, Bhuva, Svah” respectively. Thus the offerings to the gods must end with the word Svaha whereas those to the manes ends with the word Svadha.

Bhu refers to this terrestrial plane or the earth (Agni is the Lord of the Bhu loka); Bhuva refers to the solar system (Surya is the Lord of the Bhuva loka) and Svah refers to the universe beyond (Indra is the Lord of the heavens). Thus, in this earthly plane it is necessary to worship agni for a good life and energy.

Agni mantra

Traditional Bija akshara and mantra

रं
raṁ

रं जातवेदसे स्वाहा
raṁ jātavedase svāhā

Other bija  and mantra (Mantra mahodadhi)

ह्रुं
hruṁ

ॐ हुं रं चैतन्यायै नमः
om huṁ raṁ caitanyāyai namaḥ

Savitur gayatri
तत् सवितुर्वरेण्यं भर्गो देवस्य धीमहि।
धियो यो नः प्रचोदयात्॥३।६२।१०
tat saviturvareṇyaṁ bhargo devasya dhīmahi|
dhiyo yo naḥ pracodayāt||3|62|10

Agni gayatri
अग्निं दूतं वृणीमहे होतारं विश्ववेदसम्।
अस्य यज्ञस्य सुक्रतुम्॥
agniṁ dūtaṁ vṛṇīmahe hotāraṁ viśvavedasam |
asya yajñasya sukratum ||

अग्निमीळे पुरोहितं यज्ञस्य देवं ऋत्वीजम्।
होतारं रत्नधातमम्॥
agnimīḻe purohitaṁ yajñasya devaṁ ṛtvījam|
hotāraṁ ratnadhātamam||