GIRM paragraph 54
Not everybody hears a direction when it is given them. Children, dogs, my Dad, all with selective hearing. Sometimes Catholic congregations are like this also.
For example, say it is time for the "Collect," the opening prayer of the Mass. The priest says, "Let us pray." That is an instruction. It is not a cue for the Missal to be brought to him. It does not mean, "Let's get ready to pray the prayer in the book together." It means: Pray.
The brief moment of silence that follows this prayer (hopefully) is there for your use. You were anointed (if you were baptized) prophet, king, and priest. As priest, you too bring offerings and petitions to the Mass. You are not at Mass to simply to be a passive receptacle. You are not there to be entertained. You are there to work. (And if you really work, you will be surprised how much more fulfilling and quick Mass is.)
So we are instructed by the ordained priest, "Let us pray," then the priestly people, becoming aware that they are in God's presence, are to bring to the Mass the particular needs of which they are aware. A little bit later we will pray what is called the General Intercessions. Those are rather - well - general. For the Church . . . for the world . . . for all of our sick . . . these are huge blessing cans of paint thrown on the world. And yes, contained in these in some general way is the prayer that it won't rain on the parish festival, that your brother in the army will be safe, that Aunt Matilda will make it through surgery. But, at the beginning of Mass, you have the opportunity, not for a general intercession, but for a specific one: for my Brother Joe, for my Aunt Matilda who needs your healing will.
Don't hold back! The graces of every Mass are endless! Bring a whole laundry list of things! What concerns you? What troubles you? Of what are you uncertain? Don't miss this opportunity! How many more graces could be rained down upon the earth if only her priestly people would take the opportunity to ask!
And now, here is the reason the prayer is called the Collect. It is because then one of the priestly people in this congregation who is a member of the ordained priesthood collects all of those prayers (assuming he gave the priestly people an opportunity to pray and that they prayed) and offers them to the Father, through the Son, in the power of the Holy Spirit in an official prayer of the greater Church (which also serves to announce the character of the Mass,) joined with all of the prayers being offered around the world.
Don't miss out!