Over the years I have heard so many times, "I don't like going to Mass because I don't get anything out of it." While I believe we ALWAYS "get something" (grace) out of Mass (even though we may not realize it or feel it at the time), we participate in this Sunday worship because we are there primarily to GIVE something, which is the praise of God. This is part of the meaning of the commandment which says, "Keep holy the Sabbath."
Before we sing the Holy, Holy, Holy, we have a brief dialogue between the priest and the people. First the priest greets the people in the usual way with "The Lord be with you." And the people respond, "And with your spirit." Then the priest extends an invitation: "Lift up your hearts." And the people say, "We lift them up to the Lord." That is why we are there...to lift up our hearts to God. But then the priest says, "Let us give thanks to the Lord our God." And this is the purpose of our worship. To give thanks. To celebrate Eucharist.
What is the people's response? "It is right and just!" This is rather odd language for us (and was changed about 5 years ago with the revision of the Roman Missal). Where does it come from? In Greek & Roman times, it was an acclamation of acceptance. The Roman leader would announce a new law and the people would acclaim together "It is right and just!" In other words, "Yes, let's do this! It is right! It is just! It is good!" The priest then goes to say that it is indeed right and just, even our duty and our salvation, to give thanks always & everywhere. And then he says why we are giving thanks today. This is what it's all about. We give thanks to the God who provides us with everything, even with his own Body and Blood. It is right and just.