The Zoroastrian declaration of faith stands in the twelfth chapter of the Yasna, the central liturgy, and it is a confession in the strict sense: the speaker says what they are. I profess myself a worshipper of Mazda, a follower of Zarathushtra, opposed to the daevas, accepting the teaching of Ahura. Each phrase places the speaker on one side of a line.
The renunciation is as prominent as the profession, and that is characteristic. The text explicitly rejects the daevas, the beings the neighbouring Indo-Iranian tradition worships as gods, and forswears theft, violence against the settled community, and harm to the good creation. A Zoroastrian confession is not only an assent to propositions about God but an enlistment on one side of a moral struggle that the religion understands as the structure of the world itself.
Its language places it among the oldest confessional texts still in liturgical use anywhere. It is composed in Old Avestan, the stratum of the Avesta that includes the Gathas attributed to Zarathushtra himself, and it was carried orally for many centuries before the Sasanian period produced a script capable of writing the Avesta down. What a worshipper says at a navjote today is, in its wording, very old indeed.