Some time ago, Joshua sought clarification of what I wrote concerning fiducia. Let Dix explain the Proddy dogma:
"[Man] needs nothing more, can do nothing more, than be conscious of feeling that confidence in the merits of Christ's sacrifice. He must cling to that feeling of confidence, for it is all that stands between him and eternal torment. Yet even so, he must always remember that this feeling of confidence cannot really undo the terrible effects of original sin in his soul. The fact that he feels this confidence does not render anything he does or could do in itself pleasing to God. He is not in any way made holy even by 'justifying faith'; otherwise his own actions would aid in his own redemption and sanctification; grace would no more be the absolutely free gift of God, but something man had at least partially merited. He is therefore emphatically not made holy but simply 'accounted holy' by God, for the sake of Christ, whose righteousness is imputed to the believing sinner by God through a sort of fiction. But in himself the redeemed and 'justified' sinner remains an entirely sinful sinner still, and only the consciousness of his own faith in the redeeming merits of Christ stands between him and the damnation his own inescapable sinfulness entails. That is the famous doctrine of 'Justification by faith alone', which in the eyes of all protestants was the very essence of Protestantism."
Dix was vilified for what was called a travesty of the Prod dogma. But when, decades later, the ARCIC document on Justification attempted to explain and bury this old controversy, a critique published by English Evangelicals damned it on the simple grounds that they could not find in it the (for them) essential truth that "Fides est fiducia".
Hell, unless you can sustain within your gut a fervent feeling [fiducia] that Christ's merits have saved you! Scary, isn't it?. In such a preposterous perversion of the Christian faith, the Sacraments can only usefully function as tools to sustain this feeling. There is all the difference in the world between this dogma and our belief that the Eucharist is the objective reality, made present, of the Lord's One Sacrifice, so that we can enter into it, and be transformed by it.