(Those of you with sharp eyes will notice the difference between Linguam Latinam and Lingua Latina and wonder if my typing skills have failed me. Alas, no, the Latin language is rife with inflections - little tacked on endings like the -m in this example.)
The Creed is one of those five "ordinary" mass parts that I would love to have our congregation recognize, in particular its opening line: Credo in unum Deum. (That is, I believe in one God.) Many of the preludes and communion pieces that I will play this summer will be based on some of the oldest Gregorian chants of this one line of text. Be sure to notice in the bulletin when that is the case, so that your ears can start to catch the famous opening line of the Creed. The marriage of music and text can make both increasingly meaningful, I hope, so that the prelude loses its role as "background music" and becomes an elevation of prayer.
Since this entry is about Latin, I don't want to skip the point that "credo" does give rise to the modern English word "credit." But there is a vast difference between the two beliefs. I'm currently reading a finance book that spends an entire chapter on the philosophy of theories and belief. The author takes great pains to point out that his book exists to establish the truth (and hence belief) in only declarative statements that can be verified through prediction and experimentation.
The word credit (to trust or believe in the repayment of debt) is to say that by your due diligence and research you believe that someone will be capable of repaying. Similarly, to say that you believe in the theory of evolution is to say that in your mind the preponderence of the evidence is on Darwin's side. These are examples of belief based on knowledge and perhaps even understanding or comprehension. To declare a belief in God, however, as in the opening line of the Creed is to say simply that you trust, not to say that you in any way know or understand.
Why do we need Creeds? Because Christianity has a complex, nearly incomprehensible doctrine of the trinity, of a God who is fully human. We can't wrap our minds around that; we can't prove it. But we can lay out its tenets in words and song: Credo in unum Deum.