The idea of assisting at Mass always brings to mind an old adage (or perhaps quote? I forget the source).
“Don’t pray AT Mass–Pray THE Mass”
Different notions of what “active participation” really means is one of the core issues that define a Catholic as a “Traditionalist”. Many parishes have liturgy committees that really work to get the congregation to participate through singing, strong responses, and inducing a feeling of community. While these things are wonderful and necessary, they are by themselves entirely insufficient and only scratching the surface of the idea of “assisting at Mass”.
To REALLY say that you’ve assisted at Mass, sure you need to be able to say that you’ve sung the hymns and said the responses, but you also have to be able to say that you’ve MEANT every thought and word by uniting yourself (you’re WHOLE self, not just the part that sits in the pew and expels air over vocal cords in order to produce a joyful racket). This can be done a great number of ways, the simplest (and by far the most common I should think) is to contemplate the meaning of Mass and the representation of Calgary as it is played out before your eyes. Even the simple realization that it is JESUS in the priest’s hands at the Elevation(s) is a form of assisting at Mass.
I guess that the Catholic ideal of worship being a quiet and contemplative spiritual event really comes from Matthew 6:5 - “And when you pray, do not be like the hypocrites, for they love to pray standing in the synagogues and on the street corners to be seen by men. I tell you the truth, they have received their reward in full.” To me, this verse screams the notion that active prayer is private and internal, and as Catholics, we take that private and internal prayer into our Liturgies which by virtue of the nature of the Mass leaves us with an invitation to unite ourselves with the priest and God through a contemplatively prayerful attitude during the Mass.
I think I could say much more on “assisting at Mass,” but I’ve already said more than what I originally set out to.