He who sings, prays twice.
For over a thousand years, the Faithful have sung the Mass with joy. We wish to rekindle this desire to sing. After careful consideration, it has been decided by the Priests that the time is right to encourage a fuller and greater participation in the Sung Mass by the Faithful. This is not a new, modern idea. In fact, this tradition goes back thousands of years. Historically, it was a high honour to be asked to sing. And we're asking now!
Starting February 19th, members of the Choir will be positioned throughout the church for a few weeks to help us get comfortable with when to sing, and also to help give us more confidence with the parts.
BUT I HAVE A HORRIBLE VOICE!
Don't worry if you think you're awful (even those around you might think so). God is most pleased with our efforts, whether we are a professional opera singers or certified tone-deaf . If EVERYONE sings, you'll never really be heard, anyway!
I'D RATHER JUST PRAY in my own way, THANKS.
While there is merit to praying in our own way, the Mass is the most perfect prayer - and we have a rare opportunity to sing it. No doubt you have heard it said that "he who sings, prays twice". The graces are bounteous, no matter how loudly you sing (or not). It has also been proven that singing in a group sharply increases feelings of happiness and joy. Who wouldn't want happiness and joy at Mass?!
OK. I'M ON BOARD. HOW DO I KNOW WHAT TO SING?
The Hymn boards list which Mass Setting (Kyriale) and Credo that we will sing. You will alternate singing with the schola (that's the group of men upstairs who sing the gregorian chant propers). The places where we alternate are clearly marked in the hymnbook with a double line through the music. If in doubt, you'll know it's your turn when the ladies of the choir join in, and the organ gets substantially louder. Don't worry about getting it 'right'. Just "SING"!
The standing/sitting/kneeling question
The Traditional liturgists Fortescue, O’Connell, Reid, Sheen, and McManus state categorically that people should remain standing until after the Sanctus and Agnus Dei are said or sung, and rightly so, because these prayers are the Ordinary parts of the Mass that the Church has appointed specifically for the faithful’s active participation.
The Ordinary parts of the Mass are the Kyrie, Gloria, Credo, Sanctus-Benedictus, and Agnus Dei; together with the liturgical responses, they are recited or sung standing, never kneeling. Unlike in the Novus Ordo which has a “linear” liturgy that makes the celebrant wait for the conclusion of the singing of the Sanctus before he can begin the canon, the Traditional Latin Mass has a “layered” liturgy that permits the celebrant not to wait for the singing to finish before proceeding to canon. The people, however, are not to concern themselves with the parts that belong to the priest; they have their own parts assigned to them in the Eucharistic liturgy which Holy Mother Church expects them to carry out. It is, therefore, improper to kneel while the choir (and congregation) is still singing the Sanctus because the people, who are supposed to be singing it, are not yet in the canon (even if the priest is) until after the singing of the Sanctus has concluded. The same principle applies to Agnus Dei. The principle applies whether we choose to sing or not.
- The above excerpt on posture (part of a very thorough comparitive essay) taken from here