[chs68]

"The priest is like a screen with Christ as the listener and absolver."

What, again, is the real need for such a screen?

Is it that Jesus is unable to hear a confession from a penitant unless there is some sort of screen between Him and the penitant? Is Jesus too busy to hear a confession?

Or is it that the penitant is unable of knowing -- really knowing -- the he or she is forgiven unless a priest gives him or her such assurance?

[Salvation]

Here are the actual words of the priest in Absolution. You get only one guess as to who forgives a Catholic's sins in the Sacrament of Reconciliation!

Did you guess?

Here's the answer (the highlighting/bolding is mine):

 

1449 The formula of absolution used in the Latin Church expresses the essential elements of this sacrament: the Father of mercies is the source of all forgiveness. He effects the reconciliation of sinners through the Passover of his Son and the gift of his Spirit, through the prayer and ministry of the Church:

God, the Father of mercies,
through the death and the resurrection of his Son
has reconciled the world to himself
and sent the Holy Spirit among us
for the forgiveness of sins;
through the ministry of the Church
may God give you pardon and peace,
and I absolve you from your sins in the name of the Father, and of the Son and of the Holy Spirit.

[NYer]

Or is it that the penitant is unable of knowing -- really knowing -- the he or she is forgiven unless a priest gives him or her such assurance?

You have answered your own question. When we sin, we hurt not only God but others as well. Like dropping a stone into a pond, sin has a ripple effect. The Catechism of the Catholic Church summarizes this very well.

1456. "Confession to a priest is an essential part of the Sacrament of Penance: 'All mortal sins of which penitents after a diligent self-examination are conscious must be recounted by them in confession, even if they are most secret and have been committed against the last two precepts of the Decalogue; for these sins sometimes wound the soul more grievously and are more dangerous than those which are committed openly.' [Council Of Trent (1551): DS 1680 (ND 1626); cf. Ex 20:17; Mt 5:28.]  When Christ's faithful strive to confess all the sins that they can remember, they undoubtedly place all of them before the divine mercy for pardon. But those who fail to do so and knowingly withhold some, place nothing before the divine goodness for remission through the mediation of the priest, 'for if the sick person is too ashamed to show his wound to the doctor, the medicine cannot heal what it does not know.' [Council of Trent (1551): DS 1680 (ND 1626); cf. St. Jerome, In Eccl.]"
What the Catechism of the Catholic Church says on "Penance:"