The Agni Sukta is the first hymn of the Rig Veda and therefore the opening of the oldest surviving text in any Indo-European language, ascribed by tradition to the seer Madhucchandas. It is addressed to Agni, fire, in his role as the priest of the sacrifice: the god who, kindled on the altar, carries the offerings up to the other gods and brings the gods down to the offering. Fire is thus the hinge of the whole Vedic ritual, the mouth that eats the oblation and the messenger between the human and divine worlds, and it is fitting that the collection opens by invoking him.
The placement is not accidental. That the Rig Veda begins with fire, and with fire understood as the officiating priest, encodes the centrality of the sacrifice to the entire religious world the Veda belongs to. The hymn asks Agni for the goods the sacrificer seeks, wealth, protection, well-being, and addresses him with the intimacy of one approaching a household intimate as well as a god, since the same fire burns on the domestic hearth. For a tradition that would go on to interiorise and philosophise fire in countless ways, the opening hymn fixes it first of all as the practical and indispensable link between people and gods.