"You wanna lie to God? Good luck with that!"
Those words were spoken to our RCIA group by our Deacon when we had a group of candidates and catechumens discussing the (to them new) principle of Confession (more properly called the Rite of Penance and Reconciliation in Catholic teaching). One of the candidates (a former Methodist) asked "What if you aren't telling the truth when you confess to the priest?"
The deacon smiled, and said: "You wanna lie to God? Good luck with that!"
Your example person is not fulfilling the role of a sincere penitent
There are two problems with trying to deceive God during confession. Why do I mention the problem with lying to God?
Only God forgives sin
CCC 1441 Only God forgives sins. Since he is the Son of God, Jesus says of himself, "The Son of man has authority on earth to forgive sins" and exercises this divine power: "Your sins are forgiven." Further, by virtue of his divine authority he gives this power to men to exercise in his name.
It an important point to remember, since the priest is acting on Christ's behalf, and Christ is one of the three persons of the Godhead in Catholic belief. There is a detailed treatment of the Sacrament of Penance and Reconciliation here, but I'll summarize the imprtant points.
God knows what's in your heart, so He'll know that you are not truly contrite, and thus the absolution will not take effect. It is the sinner, the penitent, who has turned away from God by comitting mortal sin, thus losing baptismal grace. It is incumbent on the penitent to turn toward God in an effort to reconcile the mortal sin. Sinning again though deceit or falsehood in so doing represents a turning away from God yet again.
Technically, if the person confesses a whole host of other mortal sins in a confession to a priest, but does so under a false pretense, the have just committed another mortal sin that is unconfessed -- deliberate falsehood -- and thus needs to go to confession yet again to address that mortal sin. A vicious cycle, there is really no point in going to Confession if one is not disposed to face the Truth.
While this is an out of context quote, Jesus said "And the Truth will set you free." It's true on a lot of levels, and I'd say even moreso during confession.
If one is going to do it, it's worth doing it right
The elements of a confession are (in Catholic teaching):
- Examination of conscience.
- Be sincerely sorry for your sins.
- Confess your sins.
- Resolve to amend your life. (Act of Contrition)
- After your confession do the penance that your priest assigns.
The absolution offered by the minister takes effect after the penance is completed.
A useful guide to a proper confession is here in a USCCB hand out. There are hundreds of similar guides on the internet, and published for use in CCD, RCIA, and other teaching venues.
Additional support from the CCC
VII. THE ACTS OF THE PENITENT
1450 "Penance requires . . . the sinner to endure all things willingly, be contrite of heart, confess with the lips, and practice complete humility and fruitful satisfaction."
1451 Among the penitent's acts contrition occupies first place. Contrition is "sorrow of the soul and detestation for the sin committed, together with the resolution not to sin again."
1452 When it arises from a love by which God is loved above all else, contrition is called "perfect" (contrition of charity). Such contrition remits venial sins; it also obtains forgiveness of mortal sins if it includes the firm resolution to have recourse to sacramental confession as soon as possible.
Your example penitent is not contrite.
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."
VIII. THE MINISTER OF THIS SACRAMENT
1461 Since Christ entrusted to his apostles the ministry of reconciliation, bishops who are their successors, and priests, the bishops' collaborators, continue to exercise this ministry. Indeed bishops and priests, by virtue of the sacrament of Holy Orders, have the power to forgive all sins "in the name of the Father, and of the Son, and of the Holy Spirit."
That power to forgive comes through Christ.
1446 Christ instituted the sacrament of Penance for all sinful members of his Church: above all for those who, since Baptism, have fallen into grave sin, and have thus lost their baptismal grace and wounded ecclesial communion. It is to them that the sacrament of Penance offers a new possibility to convert and to recover the grace of justification. The Fathers of the Church present this sacrament as "the second plank [of salvation] after the shipwreck which is the loss of grace."