Credo

35. What are the most important symbols of the faith?
193-195 
They are the Apostles' Creed which is the ancient baptismal symbol of the Church of Rome and the Nicene-Constantinopolitan Creed which stems from the first two ecumenical Councils, that of Nicea (325 A.D.) and that of Constantinople (381 A.D.) and which even to this day are common to all the great Churches of the East and the West.

“I believe in God the Father Almighty, 
Creator of heaven and earth.”

36. Why does the Profession of Faith begin with the words, “I believe in God”?
198-199
The Profession of Faith begins with these words because the affirmation “I believe in God” is the most important, the source of all the other truths about man and about the world, and about the entire life of everyone who believes in God.
37. Why does one profess belief that there is only one God?
200-202
228

Belief in the one God is professed because he has revealed himself to the people of Israel as the only One when he said, “Hear, O Israel, the Lord our God is one Lord” (Deuteronomy 6:4) and “there is no other” (Isaiah 45:22). Jesus himself confirmed that God is “the one Lord” (Mark12:29). To confess that Jesus and the Holy Spirit are also God and Lord does not introduce any division into the one God.