Divorce. By itself civil divorce is not an obstacle to Communion. As a civil action all it does is settle the civil legal effects of marriage (distribution of property, custody of children etc.). However, understood as a moral action, the willful breakup of a marriage or abandonment of one’s spouse is indeed seriously wrong. The Catechism of the Catholic Church makes clear, following on Scripture, that God hates such divorce.
2382 The Lord Jesus insisted on the original intention of the Creator who willed that marriage be indissoluble. He abrogates the accommodations that had slipped into the old Law. Between the baptized, “a ratified and consummated marriage cannot be dissolved by any human power or for any reason other than death.”
2383 The separation of spouses while maintaining the marriage bond can be legitimate in certain cases provided for by canon law. If civil divorce remains the only possible way of ensuring certain legal rights, the care of the children, or the protection of inheritance, it can be tolerated and does not constitute a moral offense.
2384 Divorce is a grave offense against the natural law. It claims to break the contract, to which the spouses freely consented, to live with each other till death. Divorce does injury to the covenant of salvation, of which sacramental marriage is the sign. Contracting a new union, even if it is recognized by civil law, adds to the gravity of the rupture: the remarried spouse is then in a situation of public and permanent adultery:
If a husband, separated from his wife, approaches another woman, he is an adulterer because he makes that woman commit adultery; and the woman who lives with him is an adulteress, because she has drawn another’s husband to herself.
2385 Divorce is immoral also because it introduces disorder into the family and into society. This disorder brings grave harm to the deserted spouse, to children traumatized by the separation of their parents and often torn between them, and because of its contagious effect which makes it truly a plague on society.
Thus, those who are actually responsible for the breakup of the marriage and the failure to be reconciled when possible are indeed guilty of sin and have an obligation to repent and confess their sin before receiving Communion, as would any grave sinner.
On the other hand, of the innocent party in a divorce the Catechism says,
2386 It can happen that one of the spouses is the innocent victim of a divorce decreed by civil law; this spouse therefore has not contravened the moral law. There is a considerable difference between a spouse who has sincerely tried to be faithful to the sacrament of marriage and is unjustly abandoned, and one who through his own grave fault destroys a canonically valid marriage.
Thus, the innocent spouse in a marital break-up has the same possibility to receive Communion as other Catholics, with the usual conditions (being free from mortal sin in other areas of life, going to Confession if not, Eucharistic fast and so on).
Remarriage. As noted above in the citation from the Catechism 2382, a ratified and consummated Christian marriage is indissoluble. This is a marriage where the vows are exchanged by two baptized persons, with the proper intention, and consummated by sexual intercourse. No power on earth can declare such a marriage null and the parties free to remarry. However, a marriage tribunal of the Catholic Church is empowered to judge whether a marriage actually did occur and to issue a Decree of Nullity (popularly, but wrongly, called an annulment) when it judges it did not. (See: Annulment/Decree of Nullity) A person who receives a Decree of Nullity is free to marry in the Church since the first marriage was defective from its beginning (i.e. no marriage). A person who remarries in the Church after an annulment is free to receive the sacraments under the usual conditions (as noted above).
However, often times individuals or couples who have remarried but without a Decree of Nullity want to come into the Church, or if already Catholic approach the sacraments of Penance and Eucharist. Sometimes they are even told they can judge these matters in their own conscience without going to a Marriage Tribunal (sometimes called “the internal forum solution”).
In “Concerning the Reception of Holy Communion by Divorced-and-Remarried Members of the Faithful” the Congregation for the Doctrine of the Faith in a letter to the world’s bishops on October 14, 1994 said,
7. The mistaken conviction of a divorced-and-remarried person that he may receive holy communion normally presupposes that personal conscience is considered in the final analysis to be able, on the basis of one’s own convictions, to come to a decision about the existence or absence of a previous marriage and the value of the new union. However, such a position is inadmissible. Marriage, in fact, both because it is the image of the spousal relationship between Christ and his church as well as the fundamental core and an important factor in the life of civil society, is essentially a public reality. [/library/curia/cdfdivor.txt]
By this document the Holy See affirmed the continuous theology and discipline of the Catholic Church that those who are divorced and remarried without a Decree of Nullity for the first marriage (whether that marriage was made within or outside the Catholic Church) are in an objectively adulterous union that prevents them from honestly repenting, receiving absolution for their their sins, and receiving Holy Communion. Until the marital irregularity is resolved by a Marriage Tribunal, or other procedures which apply to marriages of the non-baptized, they may not approach Penance or Holy Communion. As Pope John Paul II pointed out in Reconciliation and Penance, the Church desires such couples to participate in the Church’s life to the extent possible (and this participation in Mass, Eucharistic adoration, devotions and so on is a great spiritual help to them), as they work toward full sacramental participation.
A Unique Case. One final situation is that of those who have repented of their illicit union, but remain together for a serious reason, such as for the sake of their children. Catholic pastoral practice allows that IF their pastor judges that scandal can be avoided (meaning most people are unaware of their remarriage and consider them a married couple), then they may live together as “brother and sister” (without any sexual relations), and be admitted to the sacraments. If scandal can not be avoided, then they must either separate or refrain from the sacraments.
Answered by Colin B. Donovan, STL