The following should help Eastern Catholics determine when they should seek sacramental confession, that is, the Mystery of Repentance.

1. The Scriptures teach that there is a basic undercurrent of sin in everyone’s life, “for all have sinned, all have fallen short of the glory of God” (Rom. 3:23). At the same time, it teaches there are distinctions in sins.
2. In distinguishing among sins, the Eastern Churches have employed the distinction between sins and transgressions. A sin would be considered a misdeed committed deliberately and with knowledge. A transgression would be an action which may be as wrong objectively, but is committed inadvertently or in ignorance. It is this distinction which is employed in many liturgical prayers. In the Divine Liturgy, we pray, “have mercy on me and pardon my offences: the deliberate and indeliberate, those committed in word and in deed, whether knowingly or unknowingly….” This to insult someone deliberately or to maliciously destroy his property would be a sin; to hurt someone’s feelings unintentionally or to accidentally break a favorite item would be a transgression. The other person would still be hurt, but inadvertently. In either case, the image of God in us has been scratched and disfigured, but sins committed in malice are clearly more serious to our spiritual condition than those committed from weakness of unconsciously.
3. Minimalism would be content with avoiding the more serious offense while ignoring the lesser: “It’s only a venial sin,” or, “I didn’t mean it so it’s just a transgression.” However, a person who is serious about deepening his relationship with God is concerned with anything which will affect that relationship or cause love to grow cold.
4. In distinguishing among sins, the Western Church has favored the distinction of mortal and venial sins. To borrow an image from the Psalms, all sin is slipping down a slope. Slipping so far or falling so rapidly that relationship with God is ruptured would be mortal sin. Venial sin would be a slower slipping or a separation not as distant.

In essence, then, a Christian should seek sacramental confession (the Mystery of Repentance) at least when he or she has sinned mortally. But this, of course, is a minimum. Anyone who is aware of serious sin is to receive the sacrament of penance as soon as possible; it is strongly recommended to all the Christian faithful that they receive this sacrament frequently especially during the times of fasts and penance observed in their own Church sui iuris.
 
 
Text excerpted from Shown to be Holy: An Introduction to Eastern Christian Moral Thought (Eastern Catholic Diocesan Directors of Catechesis, 1990). The purpose of this material is to be descriptive in respective to the issues it addresses. While the material is accurate, it is not definitive. Neither is it legalistic in its intent not does it pretend to be normative. It is shared in response to the queries posed in regards to the church’s ancient traditions. All people should seek out and defer in humility to the guidance of their priest, bishop, and Church.