At the last theology in the bar for this semester, Fr Tim spoke of the sacrifice of the Mass. We are very used to the idea of going to Church so w can be fed and nourished, both in God's Word given in scripture, or in the flesh and blood of Jesus in Holy Communion.
But our incredible dignity as Christians is revealed when we share in the sacrifice of Jesus made present in the Eucharistic prayer, made present for us through the consecration of the bread and wine which become the body and blood of Christ.
We do not just receive the fruits of that offering of Jesus - we receive the sacrifice itself, our lives become sacrifice. As we enter that mystery of Jesus dying in love for the whole human race, we are not just passive, but actively participate. If we are suffering, we can unite our suffering with his, so he can use it in his saving love. We can offer that mystery of the cross for those we love, for ourselves, or for the salvation of the whole world.
When we understand what's going on in the Mass, it's strange to think in terms of 'Sunday obligation' at all - what better place can there be, than in that mystery of the love of the Trinity bursting forth on the cross!