First of all, what is the Mass. It is the unbloody sacrifice of Calvary re-presented.
The question arises - are we "re-sacrificing Christ"? Was Christ's sacrifice not enough?
So to get to the heart of the matter - if the Mass is an "unbloody representation of the sacrifice of Calvary, wouldn't Good Friday be the PERFECT day for Mass?"
A friend from the seminary, Fr. Ryan Erlenbush, has some great things to say about this on his blog. (You can read the whole article by clicking here.) He notes:
"Precisely because the Mass is a sacrament, it is a sign (not a mere sign, but a sign which contains a reality). However, in the commemoration of the Passion on Friday of Holy Week, the reality of the sacrifice is presented to the faithful not as a sacrament (i.e. not through the Mass) but “as it was really accomplished.” The Good Friday liturgy is, in fact, a more perfect re-presentation of the sacrifice of the Cross than is the Eucharistic liturgy. The Catholic faithful are more perfectly united to Calvary on Good Friday than they are by the offering of the Mass on any other day of the year. ..
...Not of course, that there is anything lacking in the Eucharistic sacrifice offered every other day; but the Church, on Good Friday, recalls (with a special efficacy) the Lord’s Passion in its reality and not in its figure... There is no defect in the Eucharistic sacrifice: It is real and true, as a sacramental reality (and the sacraments are certainly real)....Still, on Good Friday, the sacrifice of the Cross is offered and commemorated not as a sacrament (that is, not as a figure or sign), but in the reality of its proper species – “as it was really accomplished.” Thus, just as the figure passes away in the advent of the reality, the Church does not offer the sacrifice of the Mass at the Good Friday commemoration of our Lord’s Passion.