The purpose of creeds was to take overarching narrative of the regula fidel (rule of faith) and translate it into a list of key beliefs to be affirmed. In the case of the Apostle's Creed, this meant affirming the essential narrative moments of the story of God, Jesus, and the church as part of one's formal consent to the apostolic faith before entering baptism. The primary function of the Niceno-Constantinopolitan Creed was to clarify the Christological foundation of the church's faith by expounding the precise relation between the Father and Son in terms of their shared essence and distinctive persons.
At every point of affirmation, we find that the creeds are simply summarizing what is stated in Scripture or else following the logic of Scripture to explain who God is and what he has done for us in Jesus Christ. The creeds tell us the story of faith and what parts of the story matter the most. Viewed this way, the creeds are then a type of gold standard by which one can safeguard the fixtures of our faith that are of first importance and warn against falsehood by those who would dangerously fiddle with crucial facets of the faith.
Adapted from What Christians Ought to Believe: An Introduction to Christian Doctrine Through the Apostles Creed by Michael F. Bird
The Necessity of Confessions
Creeds and Confessions are Expressions