You are standing at the edge of the pool. Crazily enough you are at the deep end! You've never even thought about going in the deep end before but here you are and Dad is in the water facing you with his arms out and he says, "Come on, I'll catch you. You'll be Okay. Be brave."
But when you jump - that's it! There is no turning around, nothing to grab on to, it's pure trust that Dad is going to save you or you drown. So you hesitate. Then Dad says, "Do you trust me?"
"Uh huh." It comes out softly.
That was a profession of faith and you gave it just before you jumped. As a matter of fact, it allowed you to jump. Saying it out loud reminded you that you believe that this mythic creature known as Dad will keep you from being obliterated. You simply need to listen, trust, jump, and maybe for a moment you will be under, for a moment that seems a lifetime there is nothing touching your body but air and then cool water, and then two firm hands raise you up eyes twinkling with pride.
So think of this: There are two parts of the Mass. There is Liturgy of the Word and the Liturgy of the Eucharist. In the first part we are instructed about the life of faith. In the second we jump into the void: heaven and earth collide, the visible and invisible meet, (if this were Star Trek, matter and anti-matter would be touching) time is warped, worlds collide, events slide into each other. It is absolutely ridiculous that we come to Mass and sit behaving in our pews in our Sunday finest. We should lashed into our pews in riot gear, ushers should come down the aisles with life preservers, and warning sirens should be going off. If we really understood what was going on we should be scared witless. We are entering the deep end!
BUT, before we do, while we are still standing on the edge getting ready to jump in, we tell God, "I trust you - I believe in you." "I believe in one God, the Father the Almighty . . . " It is this profession of faith that allows us to jump. Saying it out loud reminds us that we believe in this wonderful God known as the Father Who will keep us from being obliterated. We listened, trusted, and are preparing to jump in hopefully with our heart and mind fully understanding what it is that we are doing.
This profession of faith is said on Sundays and more solemn celebrations. It is preferred that it be sung (when was the last time you heard THAT outside of an extraordinary form Mass?) and is to be intoned by the priest UNLESS it seems more appropriate for it to be intoned by a cantor or choir such as a case where a priest cannot carry a tune a bucket.
It is to be sung or recited by all, or alternated between choir and people, or done by two choruses meaning, for example, the left side of the church says a stanza then the right side of the church says a stanza.