अग्निमीळे पुरोहितं agnimeele purohitam....

अग्निमीळे पुरोहितं यज्ञस्य देवम् ऋत्विजं होतारं रत्न धातमम्

agnimīḻe purohitaṁ yajñasya devam ṛtvijaṁ hotāraṁ ratna dhātamam

1 -1-1 of Rigvedam.

We do not know whether this is the first Vedic Mantram uttered by man.. But it is placed as the first Mantram, in the First of the Vedas, namely Rigvedam.. as it has come to us..

This mantram is in praise of The God of Fire Agnideva

The worshipper is acutely conscious of the supremacy of the most potent force of nature that is manifest near him

He treats fire as the Primordial priest, who leads the mortals safely ahead in spiritual and temporal Life.(Purohita)

Of course, Agni is one of the deities who is offered His share in Yajnams by way of ghee and cooked grain and other offerings.. in addition Agni acts as the carrier of the offerings made to other Gods

Ritvik The official in the yajna who looks after the procedural aspects.

Hotaaram.. The official in the Yajna who invokes and invites the presence of deities who are being worshipped.

Ratnadhaatamam.. Repository of wealth.. and Agni is capable of making His worshippers too rich in wealth..

So the Plain meaning is 

I worship Agni who is the priest, the one who leads us from the front, who is the deity subject matter of a ritual, a yajna who is the one who makes the formal invocations in the yajna who is the source, storehouse and the bestower of all wealth, gems, precious stones etc 

A simple word analysis..

अहम् I

पुरोहितम् the priest, the one who leads us from the front

यज्ञस्य् देवम् the deity subject matter of a ritual, a yajna 

ऋत्विजम् the ritvik.. who conducts and supervises the procedures of Yajna

होतारम् the one who makes the formal invocations in the yajna रत्नधातमम् who is the source, storehouse and the bestower of all wealth, gems, precious stones etc 

अग्निम् The God of Fire Agni 

ईळे ईडे। Praise, takes side with praises and for refuge..

aham purohitam yajñasy devam ṛtvijam hotāram ratnadhātamam agnim īḻe īḍe |

Note.. This is a mantram which has been commented upon by the greats like Saynaacharya and Bhattabhaskara and others.. There are so many notations, so many implied meanings.. So what I wrote above is too rudimentary.

This post is just by way of introduction to a great subject in study of Sanskrit.. The Vedas..