From Stephen Pressley's chapter on Hope in the Early Church in Cultural Sanctification, 147:
Confessing this rule at baptism was the performative act that not only affirmed the divine narrative but acknowledged one's place in it. When they made this confession and joined the church, new believers were stepping out of the water and onto the land of a new reality.
Those joining the church would affirm the two bookends in the rule of faith: belief in "one God, the Father Almighty, Maker of heaven and earth, and the sea, and all things that are in them," and also belief in the judgment of the reprobate and the hope that the righteous will be surrounded with everlasting glory.
The rule of faith thus had a narrative thread that sewed together the beginning and end of things and put Christians in its line.