First, the traditional teaching is that a valid confession forgives all mortal sins, including those genuinely forgotten. The penitent has the obligation to mention the forgotten sin at their next confession once they remember it, but the sin itself is already forgiven.
Second, it is always acceptable to receive Holy Communion, unless you are truly conscious of unconfessed mortal sin. You cannot be guilty of mortal sin (and, therefore, in a state of mortal sin) without knowing whether the matter is grave/serious/objectively mortal to begin with. This is what you wanted to ask the priest about. Therefore, because you were unsure that the matter was mortal, then by definition, you could not be guilty of mortal sin in that particular instance. So it was perfectly acceptable for you to receive Holy Communion.
Mortal sin is thumbing your nose at God. A person committing a mortal sin knows that God has forbidden that act but he decides to do it anyway. A person who is honestly ignorant about the seriousness of the sin (in God's eyes) does not commit a mortal sin. The sin would be venial, in that case. Venial sin is still very bad and should always be avoided, but it should not keep you from receiving Holy Communion.
That's right. If you made a good examination of conscience and have true contrition, you make your confession telling all mortal sins that you can recall. You receive absolution and are cleansed of sin and can approach the sacrament of Communion. If you remember a mortal sin that you forgot, you are obliged to confess it next time, but it is forgiven. Thats why it's good to say "for these and for all the sins of my past life, I am heartily sorry". Also if you don't have time to say your penance before going to communion, you can say it after and the sins are still forgiven.
On Ignatian retreat, the priest said "okay you have made your general confession and you are about to approach the communion rail. No doubt the devil is going to whisper in your ear a sin you forgot and you will be afraid to receive. Or he may say that you didnt describe a sin properly. This is scruples." If you remembered an unconfessed mortal sin, you tell it to the priest in the next confession and mention that you forgot it in the last confession.
Topic: Recieving Communion (Read 12064 times)