The Creed has the Authority of Scripture Behind it
Cyril became Bishop of Jerusalem in 350 and is known for his systematic catchesis which he used to instruct new converts to Christianity in the essentials of the faith as part of their preparation for baptism at Easter and for further instruction on spiritual formation in the week following. Cyril's writings are filled with the loving and forgiving nature of God, the healing power of forgiveness and the companionship of the Holy Spirit.
The faith which the Church hands down to you has all the authority of the Scriptures behind it. This is the faith, and none other, which you must learn to proclaim and in which you must persevere. Our spiritual life must not be put at risk through ignorance, and since there are some who do not read the Bible, either because they are too busy or because they are illiterate, the essence and core of our faith has been captured, and can then be memorized, in the few short lines of the Creed.
Keep this faith ever by your side to help you on your way and close your ears and have nothing to do with any other, even if I myself should change my allegiance and preach another faith to you, or an angel of darkness be transformed into an angel of light to lead you into error. Even if we or an angel from heaven should preach to you a gospel contrary to that which we preached to you, let him be accursed.
To begin with, simply take the words as they stand at their face value, put your faith in them and commit them to memory. Later, as opportunity offers, you can take the propositions one by one and study them as truths of the sacred Scriptures. This summary of our faith is not a merely human composition but the more striking sayings of the Scriptures have been assembled together to form one comprehensive statement. And as a small mustard seed carries within itself the potential of large branches, so the words of our creed are pregnant with the whole content of our religion as it is expressed both in the Old and New Testament.
Pay attention then, brethren, to the truths of faith now being handed down to you and write them deep in your hearts. Keep a careful watch and be on your guard against foes and heretics intent on perverting your faith and plundering it. You must as it were deposit this gift of faith in the bank for safe-keeping and God will demand of you an account of your investment. In the presence of God, who gives life to all things, and of Christ Jesus, who in his testimony before Pontius Pilate bore witness to that great claim. I charge you to keep the faith unstained until the appearing of our Lord Jesus Christ.
You have been entrusted with an immortal treasure and the Lord will require an account of it from you at the time of his appearing, and this will be made manifest at the proper time by the blessed and only Sovereign, the King of Kings and Lord of Lords, who alone has immortality and dwells in unapproachable light, whom no man has ever seen or can see. To him be honour and eternal dominion! Amen.
Cyril of Jerusalem (313-386)
1 Timothy 6:3-16