The Greek word symbolon meant half of a broken object, for example, a seal presented as a token of recognition. the broken parts were placed together to verify the bearer’s identity. the symbol of faith, then, is a sign of recognition and communion between believers. Symbolon also means a gathering, collection or summary. A symbol of faith is a summary of the principal truths of the faith and therefore serves as the first and fundamental point of reference for catechesis.
The first “profession of faith” is made during Baptism. the symbol of faith is first and foremost the baptismal creed. Since Baptism is given “in the name of the Father and of the Son and of the Holy Spirit”, The truths of faith professed during Baptism are articulated in terms of their reference to the three persons of the Holy Trinity. and so the Creed is divided into three parts: “the first part speaks of the first divine Person and the wonderful work of creation; the next speaks of the second divine Person and the mystery of his redemption of men; the final part speaks of the third divine Person, the origin and source of our sanctification.” These are “the three chapters of our [baptismal] seal”.
From the Catechism of the Catholic Church 188-190