Regarding the disagreement between DavidFilmer and thistle, I offer this:
from EWTN.
"A catechist from Michigan asked if candidates in the RCIA may receive the sacrament of penance before they have been formally initiated into the Church.
"In this case we are dealing with Christians validly baptized but who have not yet made their solemn entrance into the Catholic Church nor received the sacraments of confirmation and Eucharist.
"This case is already foreseen in the appendix to the Introduction to the Rite for the Christian Initiation of Adults.
"Norm No. 9 stipulates that if the candidate is to admitted to the Catholic Church during Mass (the usual practice), then beforehand, the candidate, having considered his personal condition, confesses his past sins after having informed the priest of his proximate admission.
"Any priest with faculties for hearing confessions may receive this confession.
“Thus, not only may the future Catholic make his confession before being formally received but in general he or she should do so.”
Thus there is no question regarding the canonical legitimacy of the practice described. Yet, this does not answer the theological difficulties experienced by our reader.
Perhaps an answer could be found by making a distinction between impediments to the valid reception of a sacrament stemming from divine law and those stemming from Church law.
From the point of view of divine law, baptism is absolutely necessary before receiving any other sacrament. Once baptism has been received, however, the person has at least the root possibility of receiving some of the other sacraments even though other impediments might exist.
A person baptized as a Protestant (Eastern Christians are in a very different position) is usually impeded from receiving the sacraments of confirmation, Eucharist, penance, anointing and holy orders due to their lack of communion with the Catholic Church.
The Church usually recognizes the sacramental quality of any valid marriage between a baptized man and woman.
Since most of the impediments to valid reception of these sacraments by non-Catholic Christians are rooted in Church law, not divine law,
the Church itself may decide under what conditions a person not within her fold may receive the comfort of some of her sacraments and thus lift the impediment to invalidity.
Such conditions are set out, for example, in the Ecumenical Directory, and usually require grave conditions such as danger of death, the spontaneous request of the person desiring the sacrament, and faith in the Catholic understanding of the sacrament by the person requesting it.
In the case of the person who is about to be received into full communion, the Church creates, so to speak, an automatic exception which makes the sacrament of reconciliation both valid and licit for the person involved.
Canon Law:
Can. 840 The sacraments of the New Testament were instituted by Christ the Lord and entrusted to the Church. As actions of Christ and of the Church, they are signs and means by which faith is expressed and strengthened, worship is offered to God and our sanctification is brought about. Thus they contribute in the most effective manner to establishing, strengthening and manifesting ecclesiastical communion.
Can. 841 Since the sacraments are the same throughout the universal Church, and belong to the divine deposit of faith, only the supreme authority in the Church can approve or define what is needed for their validity. It belongs to the same authority, or to another competent authority … to determine what is required for their lawful celebration, administration and reception and for the order to be observed in their celebration.
Can. 843 According to their respective offices in the Church, both pastors of souls and all other members of Christ’s faithful have a duty to ensure that those who ask for the sacraments are prepared for their reception. This should be done through proper evangelization and catechetical instruction, in accordance with the norms laid down by the competent authority.
Can. 844 Catholic ministers may lawfully administer the sacraments only to Catholic members of Christ’s faithful, who equally may lawfully receive them only from Catholic ministers, except as provided in §2, 3 and 4 of this canon and in can. 861 §2.
Catholic ministers may lawfully administer the sacraments of penance, the Eucharist and anointing of the sick to members of the eastern Churches not in full communion with the Catholic Church, if they spontaneously ask for them and are properly disposed. The same applies to members of other Churches which the Apostolic See judges to be in the same position as the aforesaid eastern Churches so far as the sacraments are concerned.
If there is a danger of death or if, in the judgment of the diocesan Bishop or of the Episcopal Conference, there is some other grave and pressing need, Catholic ministers may lawfully administer these same sacraments to other Christians not in full communion with the catholic Church, who cannot approach a minister of their own community and who spontaneously ask for them, provided that they demonstrate the catholic faith in respect of these sacraments and are properly disposed.